What is joy? How is it different from happiness (or is it)?

Happiness can come and go based on our circumstances. However, biblical joy does not depend on circumstances and should be experienced at all times.

So also you have sorrow now, but I will see you again, and your hearts will rejoice, and no one will take your joy from you. John 16:22

The joy spoken of by Jesus here is a joy based on the fact that they would see Him again after He had "gone away". He was going away to die on the Cross. The significance of them seeing Him again was that it would be after His resurrection. Then they would know that death had been defeated, the sacrifice was complete, Jesus would reign, and men and women could truly be declared righteous.

That's why Paul could say:

More than that, we rejoice in our sufferings, knowing that suffering produces endurance and endurance produces character, and character produces hope, and hope does not put us to shame, because God’s love has been poured into our hearts through the Holy Spirit who has been given to us. Romans 5:3-5

Joy (or rejoicing) is still present in the midst of suffering, even when you're not happy about your circumstances.

I think joy can be equated to happiness, but the problem as you pointed out may be what we consider to be happiness. I like to think of joy as spiritual happiness.

The world views happiness as having what you want. Joy as used in the verses you referenced means being happy in having what you need spiritually. In a spiritual sense, what we need is to be in a relationship with God.

By pursuing worldly needs, we may be able to make ourselves happy for a time, but we won't be fulfilling our spiritual needs. By pursuing God we will fulfill our spiritual needs and can experience true joy.

From another perspective, when someone is unhappy, it's usually because they are lacking something they want. When you stop wanting the worldly goods, you will have no reason to be unhappy! You can be filled with perfect joy!

God is love. God loves his creation, his progeny, mankind, God is all merciful. God makes the rain to fall upon all; God saves; God is the source of every good and perfect gift. God created the heavens and the earth; God created all the elements, the atoms, the electrons, the quarks and subatomic particles; God made this time space reality, the planets, the solar systems, the galaxies, the universe. God created the DNA code blueprint shared by all life; God is the creator and source all life including all of us. Creation and expansion and growth has never stopped; you and I were passed the miraculous gift of life the the giver of life which

The recently elevated Saint Paisios the Athonite who, before he became a monk, was a WWII radio operator, said God is broadcasting 24/7. Our job is to become a tuner, and tune ourselves to his channel. That channel, that frequency, is joy, appreciation, love. Agape or uncondition love: means being in a state of joy, appreciation, love, happiness from the inside out, regardless of what is going on outside of us. To be loving, joyful, appreciative—in the face of any condition, whether like Viktor Frankl in a Nazi concentration camp or Solzhenitsyn in a gulag, when we can find something to appreciate, be joyful, then we have found, tuned ourselves, to God’s frequency.

You and I began as a single cell: we were given a gift from our mothers and fathers of half strands of living DNA that in the spirit of love and joy joined. The force which created worlds created us: that single cell divided and multiplied into 37.2 trillion cells, cells which continue to be born and live and die and replicate every day of our lives. Is that not a miracle of creation?

Being in a state of joy, unconditionally, is to be in alignment with God, to be tuned to His channel. This is why the martyrs died happily or the wild animals befriend the saints: God is love and when we become love, when we align to his frequency, all fear is gone.

Joy and Happiness can mean the same thing. In the verses you linked to, joy is linked to spiritual happiness, not happiness here on earth.

We are most definitely not promised an easy life once we become a Christian. Quite the opposite, we're promised trials and tribulation. (John 16:33, James 1:2-8) Yet in Romans 8:18, Paul says (KJV)

For I reckon that the sufferings of this present time [are] not worthy [to be compared] with the glory which shall be revealed in us.

Our joy comes in our expectation of what the next life will be like, when we will dwell with God in Glory, and in knowing that we are saved from eternal damnation.

If you've never heard it, Ray Comfort has a teaching called "Hell's Best Kept Secret". In it, he uses an illustration of two passengers being given a parachute on a plane.

• The first is told to put it on because it would improve his flight. (Akin to telling people that becoming a Christian will bring you happiness here on earth.)
• The second is told to put it on because any minute, he'd be jumping feet from the plane.

In it, the first one eventually takes it off because it does nothing to improve his flight. It's uncomfortable, heavy, and the other passengers laugh at him.

The second one barely notices the weight of the parachute, or the uncomfortableness. Instead, his mind is consumed with the thought of what would happen if he had to jump without it, and as a result he barely notices the other passengers mocking him, and he has a deep rooted sense of joy and peace, knowing that he's safe from sure death.

When I read of Joy in the new Testament, I think of that second passenger. The joy comes from gratefulness to God for salvation, not a lack of trials or an "easy" live here and now.