Can we be united in prayer?

The answer is Yes, the gospel and the Apostolic teachings are very clear, God the Father the creator of all mankind desires all His children to be united as one.

John 17:20-22 New International Version (NIV)

Jesus Prays for All Believers 20 “My prayer is not for them alone. I pray also for those who will believe in me through their message, 21 that all of them may be one, Father, just as you are in me and I am in you. May they also be in us so that the world may believe that you have sent me. 22 I have given them the glory that you gave me, that they may be one as we are one.(John 17:20-22 New International Version)

Jesus Christ said it clearly that He is praying that those who believe in Him regardless of denominations or groups may be together or be united as one.

St.Paul the Apostle to the Gentiles teaches in the Council of Jerusalem that all Jews must embraced the converted gentiles as their brothers in Christ.

Sons Through Faith in Christ …27*For all of you who were baptized into Christ have clothed yourselves with Christ. 28There is neither Jew nor Greek, slave nor free, male nor female, for you are all one in Christ Jesus. 29And if you belong to Christ, then you are Abraham’s seed and heirs according to the promise* (Galatians3:27-29)

How about the people who do not believe or professed their faith in Jesus Christ is Lord, like the Jews, Muslim, Hindus, Buddhist, etc...

The Catholic Church at the Second Vatican Council was inspired by the Holy Spirit and was given the wisdom to call our brothers and sisters belonging to different faith & religion who have goodwill as People of God too. Their faith contain the element of Truth too, but not in the fullness of Truth.

Pope Francis recent controversial teachings gave us a clear explanation and hope, that unity in diversity can be realized if one will respect our cultural differences and faith expression, after all, all of us belong to only One Maker.

"The pluralism and the diversity of religions, color, sex, race and language are willed by God in his wisdom, through which he created human beings,"(Pope Francis)

Pope Francis had shown to all the world that unity is possible, and a good example is the signing of the Fraternal Charity Agreement with the Muslims.

Pope Francis and Sheik Ahmed el-Tayeb, grand imam of al-Azhar, a leading authority for many Sunni Muslims, stepped into the debate Feb. 4 when they signed a document on "human fraternity" and improving Christian-Muslim relations.https://www.ncronline.org/news/theology/does-god-want-religious-diversity-abu-dhabi-text-raises-questions

Pope Francis continues what St.John Paul II and Pope Benedict XVI had embraced that originated in the Second Vatican Council teaching called Nostra Aetate.

DECLARATION ON THE RELATION OF THE CHURCH TO NON-CHRISTIAN RELIGIONS NOSTRA AETATE PROCLAIMED BY HIS HOLINESS POPE PAUL VI ON OCTOBER 28, 1965 http://www.vatican.va/archive/hist_councils/ii_vatican_council/documents/vat-ii_decl_19651028_nostra-aetate_en.html

The only question is, what kind of prayer can all the people gathering as one in united prayer will utter, what will the people pray?

The People of God must pray together imploring the Will of God to be done here on earth as it is in Heaven. What is the Will of God?

Instructions on Worship 2 I urge, then, first of all, that petitions, prayers, intercession and thanksgiving be made for all people— 2 for kings and all those in authority, that we may live peaceful and quiet lives in all godliness and holiness. 3 This is good, and pleases God our Savior, 4 who wants all people to be saved and to come to a knowledge of the truth. (1Timothy2:1-4)

But before the People of God can pray harmoniously as brothers & sisters in Christ and acknowledged the One Creator and Father of all Mankind, the Father of Jesus Christ. The People of God must destroy first the enemy of unity of the Church of Christ because it is the Will of God from the very beginning decreed after the Fall of Man.

"I will put enmities between thee and the woman, and thy seed and her seed: she shall crush thy head, and thou shalt lie in wait for her heel." (Genesis3:15 Douay Rheims)

Unless, the old serpent proud ugly is crushed first, then the People of God cannot enter the New Paradise wherein they would come together united as one praising and glorifying God in the presence of Jesus Christ.

So, what is the prayer that the People of God must pray together?

1. The People of God must unite in prayer to command the old serpent to go to the Foot of the Cross and reminded him the the blood of Christ has already defeated him. The unity prayer must foster charity or love to vanish hatred from the hearts of men.

2. Jesus said, when two or more are gathered in my name there I am in their midst. (Matthew18:20). The People of God can pray together what Jesus had taught in the gospel, the "Our Father Prayer".

3. The third prayer, that was proven many times to defeat enemies of the Church is the Holy Rosary. Praying the Holy Rosary together will bring the Peace of Christ to the world as promised by Our Lady in Fatima and continued in Medjugorje, the Our Lady Queen of Peace.

But, the most powerful prayer that Jesus Christ had taught us to pray and implore, was the revelation Jesus made to St.Faustina. The People of God united in prayer as one must implore this prayer;

"Eternal Father I offer Thee the body, blood, soul and divinity of your dearly beloved Son our Lord Jesus Christ in atonement for our sins and those of the whole world".

"For the sake of His sorrowful passion, have mercy on us and of the whole world."

All Catholic, Christians, Jews, Muslims, Hindus, Buddhist, Jehovah, etc..must pray together as one "to lift-up" Jesus Christ as the only pleasing and acceptable sacrifice to God to implore the Infinite Mercy of God for the conversion of all sinners.

"Now judgment is upon this world; now the prince of this world will be cast out. And I, when I am lifted up from the earth, will draw all men to Myself.”

As Pope Francis said;

"The Divine Mercy of God is Infinite but the Time of Mercy is Not."

Disunity over different views of God

When two denominations have fundamentally different views of God, for example trinitarians and non-trinitarians, they will generally not be willing to pray with each other. They may however be willing to pray next to others at ecumenical services as long as they think it will not give the impression that their gods are the same. For example if they are invited to an ecumenical service after some big natural disaster. But many Christians would not be willing to participate in such an event.

Theological differences preventing joint prayer

Sometimes two groups of Christians will recognise each other as true Christians, but there will be theological differences that mean that sometimes they will not be able to join together in prayer.

For example: infant baptism. Some infant baptists teach that the child of believers is born a member of the church; while many paedobaptists would disagree. At an infant baptism service a paedobaptist may not join in all the prayers if they affirm something they do not believe is true, but they would still join in the part of prayers that asks God to guide and protect the child as they grow up.

Or for another example, a Protestant would not join in many of the prayers of a Catholic mass, but they may still join in prayers at other parts of a Catholic service. Similarly Catholics and Protestants can pray generally for each other's missionaries that God would bring people to know him through their ministries, but may not feel comfortable praying for specific prayer points from a missionary if they concern an aspect of ministry they do not believe is wise or reflectful of the truth. The same could be said for cessationalists and Pentecostal missionaries.

If two groups of Christians are given the opportunity to write the prayers together then it is likely they will be able to find a way they can pray together. But if just one group is in charge of the content of the prayers, then other groups may not be able to join in prayer with them.

Can we be united in prayer?

The short answer is yes.

In fact we should do so in imitation of Our Lord by following his very example.

Jesus Prays for All Believers

20 “I do not pray for these alone, but also for those who will believe in Me through their word; 21 that they all may be one, as You, Father, are in Me, and I in You; that they also may be one in Us, that the world may believe that You sent Me. 22 And the glory which You gave Me I have given them, that they may be one just as We are one: 23 I in them, and You in Me; that they may be made perfect in one, and that the world may know that You have sent Me, and have loved them as You have loved Me. - John 17: 20-23

If Jesus prayed that all Christians should be united, who are we not to follow the Lord’s very example.

Some souls have offered their very substance for the unity of Christians. Blessed Maria Gabriella Sagheddu, O.C.S.O. (17 March 1914 - 23 April 1939) spent much of her life praying for the unification of all Christians.

Pope John Paul II referred to her in his papal encyclical Ut Unum Sint in which he said:

Praying for unity is not a matter reserved only to those who actually experience the lack of unity among Christians. In the deep personal dialogue which each of us must carry on with the Lord in prayer, concern for unity cannot be absent. ...It was in order to reaffirm this duty that I set before the faithful of the Catholic Church a model which I consider exemplary, the model of a Trappistine Sister, Blessed Maria Gabriella of Unity, whom I beatified on 25 January 1983. Sister Maria Gabriella, called by her vocation to be apart from the world, devoted her life to meditation and prayer centered on chapter seventeen of Saint John's Gospel, and offered her life for Christian unity. ...The example of Sister Maria Gabriella is instructive; it helps us to understand that there are no special times, situations or places of prayer for unity. Christ's prayer to the Father is offered as a model for everyone, always and everywhere.

After Sagghedu's death it was noted that in her bible the seventeenth chapter of John's Gospel had become yellowed and worn from being often read. It is in this chapter that Jesus appeals to the God the Father on behalf of His disciples. But of particular significance are verses 11 and 21 in which Jesus prays "that they may be one, as we also are" (John 17:11) and "that they all may be one, as thou, Father, in me, and I in thee; that they also may be one in us: that the world may believe that thou hast sent me" (John 17:21). These verses are used as a motto for the ecumenical movement.

Pope John Paul II often encouraged dialogue between different Christian Churches.

Ut Unum Sint was the first encyclical ever devoted exclusively to the ecumenical imperative. In this groundbreaking exercise of the papal magisterium, Pope John Paul affirmed that the ecumenical commitment made at Vatican II was irreversible. He taught his fellow Catholics that the quest for Christian unity ought to be sustained both internationally and in the local churches.

All Christians are invites to be united in prayer, even if other churches chose not to do so. They can nevertheless pray for unity on their own. Or as the Angel of God said on Christmas Day:

Glory to God in the highest; and on earth peace to men of good will. - Luke 2: 14

The following articles may prove helpful:

• Churches worldwide prepare for Week of Prayer for Christian Unity
• The Week of Prayer for Christian Unity: 4 Things Churches Can Do

The header question is actually a different subject from the body of the question. The body of the question is about 'large groups' and their possible 'objections'.

The head question is a fundamental issue :

Can we be united in prayer ?

I am answering this basic question. I am assuming that the 'we' is persons who confess the name of Jesus Christ among their fellow human beings and that the 'we' is persons who 'depart from iniquity'

That if thou shalt confess with thy mouth the Lord Jesus, and shalt believe in thine heart that God hath raised him from the dead, thou shalt be saved. [Romans 10:9, KJV]

Let every one that nameth the name of Christ depart from iniquity. [2 Timothy 2:19, KJV]

Jesus Christ, himself, said :

I will build my church. [Matthew 16:18, KJV.]

It is Jesus Christ who builds the church, in any generation. Humanity on earth does not and cannot do this. How could it be possible ? Shall the Church exist, anywhere and at any time, in the absence of he whose name it bears ?

What on earth would be the point ? And what kind of 'church' would it be ?

So, no, we cannot be united 'in prayer'. It is not prayer that unites. It is the living presence of Jesus Christ, the Son of God, who unites. That is to say (in the physical absence of him who rose from the dead and ascended into heaven) the Living presence, in the Person of the Holy Spirit, who (alone) conveys the real presence and the Living Person of the Son of God.

Peter said to Jesus of Nazareth :

Thou art the Christ, the Son of the living God. [Matthew 16:16, KJV]

and Jesus said to Peter :

... thou art Peter, and upon this rock I will build my church [Matthew 16:18, KJV]

This relationship is what unites Jesus and Peter : a relationship in which each one knows (and names) the other one. They know one another, in a spiritual way. And this unites them in a spiritual union. Which union is as strong and as permanent as rock.

The 'rock' is a relationship with Jesus Christ, a relationship not of flesh and blood (see verse 17) but of Spirit and by faith and by the revelation that Jesus Christ of Nazareth is, as Peter confesses at that very moment of time :

... the Son of the living God.

This is what unites. Not humans gathering together, themselves, and deciding to pray together. That will be a united gathering of disparate human beings. And, especially, it will be a gathering of persons who are deliberately setting aside some very real issues and some very pertinent matters of righteousness.

In other words, a casting away of integrity in order to be 'united'.

But that is not how Jesus Christ builds the church that is really his and the church that truly is worthy of the description : The Body of Christ.

Because what genuinely unites true believers in Christ, one with another, is the real and living and present - Person of Jesus Christ, himself.

And it is He, himself, who gathers them together.