Why do Protestants not refer to Mary by the title "Mother of God"?

Protestants do not call Mary "Mother of God" because:-

1. the title has no scriptural precedent. Is it wise to call her by a title which is not scriptural? The watchword for Protestants is "sola scriptura", Scripture only: God's Word alone is the Protestant's guide for belief and practice. No where in God's Word is Mary called "the Mother of God".

2. there is no Biblical evidence that the New Testament church bequeathed on Mary any special position. The title is often associated with the idea that prayers can be offered to Mary. But in Acts of the Apostles Mary the mother of Jesus was not being prayed to, but praying with others to God, exactly the same as all the other believers (Acts 1:14);

3. the title gives a measure of honour to biological kinship which is unspiritual (and unscriptural).

In Mark's Gospel Jesus does not do as Mary wishes, he denies there is any significant bond between himself and his mother:

'And they said to him Behold your mother and your brethren outside seek for you. And he looked round about on them which sat about him, and said, Behold my mother and my brethren!' Mark 3:31-35

This event is described in all three of the Synoptic Gospels, Matthew 12:46-50, Luke 8:19-21. For Him, those who obey God's word are closer in relation than fleshly relations.

She wants him to come outside to her and his brothers. He ignores her wish. To call her "Mother of God" is to give her a respect which Jesus certainly does not give her on this occasion. Why did Jesus not obey his mother here? His family thought he had taken leave of his senses, was out of his mind, for they said "he is beside himself" (Mark 3:21). So they come to kindly "lay hold on him" (Mark 3:21) to take him away from the crowds for his own good. Mary has probably been persuaded by her other sons to play a part in this (sinful) act of unbelief.

4. Scripture in one passage (at least) appears to actively discourage such a title:-

"For this Melchisedec, king of Salem, priest of the most high God, who met Abraham returning from the slaughter of the kings, and blessed him;

To whom also Abraham gave a tenth part of all; first being by interpretation King of righteousness, and after that also King of Salem, which is, King of peace;

Without father, without mother, without descent, having neither beginning of days, nor end of life; but made like unto the Son of God; abideth a priest continually." (Hebrews 7:1-3)

Melchisedec was a type ((or a picture)) of Christ, (some think he was a theophany). How? He was :-

1. Priest of the Most High God;
2. A King;
3. King of Righteousness;
4. King of Peace;
5. Without father;
6. Without mother;
7. Without descent;
8. Having neither beginning of days nor end of life;
9. Abiding a Priest continually.

In all these things Melchisedec was "made like unto the Son of God". What the writer is saying, speaking under inspiration, is that Jesus had no father and no mother. What does it mean?

Of course, Jesus was "5. Without father" in that he had no human father, his human nature had no father; likewise Jesus was "6. Without mother" in that he had no Divine mother, or his Divine nature had no mother.

Now someone could argue the logic of it all as Catholics do, and logically they would be right, Jesus in his united person had both a mother and a father, but the Bible is our guide, and we should stick to its language rather than make logical inferences.

Jesus also was without mother or father in the usual sense that a person who has a mother and father has a beginning. But Jesus had no beginning but "had neither beginning of days nor end of life" (Heb 7:3).

To call Mary "the Mother of God" is at least discouraged by the words of Hebrews 7:3 because Melchisedec was like the Son of God, "without mother".

5. despite what may have been the original good intention to draw attention to Christ (as God), in Protestant eyes the evidence of history is that the title has drawn attention away from Christ and onto a creature; and of our Lord Jesus God's Word says "Salvation is found in no other name for this is no other name under heaven by which we must be saved" (Acts 4:12).

6. the title is given to one who is often said to be able to sympathise with us more than our dear Saviour; and therefore, to the Protestant, the title is associated with teachings which offer deep insult to our Lord Jesus Christ (and to all the Persons of the Godhead, whose character is identical to His character):

"For we have not an high priest who cannot be touched with the feeling of our infirmities; but he was in all points tempted like as we are, yet without sin. Let us therefore come boldly to the throne of grace, that we may obtain mercy, and find grace to help in time of need." Hebrews 4:15,16.

Hebrews 4:15,16 teaches us we do not need to go to anyone else. We must go to the Throne of Grace itself, to God himself seated on his Throne, in the name of Jesus Christ, to receive forgiveness. We do not need to go to any Priest, or to Mary or to anyone else. God invites us to come boldly (that is not arrogantly but confidently, knowing he will grant us his mercy and pardon). This is what David did (Psalm 32:5), and God forgave him. Sadly, the Roman Catholic Church leads needy sinners away from God and his goodness.

The Son went to great lengths to find his lost sheep (Luke 15:4-7) dying in their place; and we have a Father who ran to meet us (Luke 15:20) whose "compassions fail not" (Lamentations 3:22); and the Holy Spirit is our Comforter (John 14:16).

7. to the Protestant, the title is associated with teachings which give a false comfort, because they are neither based on Scripture, nor on faith in Christ alone, nor on a life-changing turning away from sin and back to God. Jesus, and only Jesus, "is able to save to the uttermost all who come to God by him, seeing he ever lives to make intercession for them" (Heb 7:25). We must come to God, and we can only do that through believing on Jesus Christ and on his death for all our sins.

The Scriptures teaches "There is one God and one mediator between God and men, the man Christ Jesus." (1 Timothy 2:5) and

Our Lord says: "No man comes to the Father except through me." (John 14:6).

In short, the Scriptures say that "all men should honour the Son even as they honour the Father" (John 5:23), but it nowhere says that "all men should honour the Mother even as they honour the Son".

There are two things going on here, one theological and one sociological.

Theologically, there are certainly Protestants who would call Mary the Mother of God. As noted in the comment, the key term is the Greek word Theotokos. The teaching of the Council of Ephesus is that since Christ is God, and since Mary is the mother of Christ, Mary is the mother of God. This council is accepted as authoritative (or at least its teachings are accepted) by large swathes of Protestant Christianity.

The sociological thing is a Protestant aversion to venerating or even honoring Mary. You could call this anti-Catholic bias, or you could call it a simple reaction to Protestantism's Catholic roots, but for whatever reason, it is what it is. (Another example is that Protestants have mined the whole of the Old and New Testaments for biblical names for girls, but almost never choose “Mary”.)

I will add personally that, as a Protestant, the term “Mother of God” made me cringe, but when learned about the origin of the controversy—which is after all about Christ, and not about Mary at all—the point became quite obvious to me.