All must surely agree that it is impossible to read through the New Testament without seeing that this [joy] is to be the supreme think in the Christian life.
It must of necessity be so, because if this gospel is true, that God sent His own Son into the world to do for us the things that we have been considering, then you would expect Christians to be entirely different from unbelievers; you would expect them to live in a relationship with god that would be evident to all, and that should above everything else produce this quality of joy. […]
Hence we find this constant exhortation in the New Testament to praise God and offer up thanksgiving. This is what differentiates us from the world. The world is very miserable and unhappy; it is full of cursing and complaints. But praise, thanksgiving and contentment mark out the Christian and show that he is no longer “of the world.” (Vol. 1, p. 49)
-Martyn Lloyd Jones, “The Everlasting Covenant” in God’s Eternal Purpose: An Exposition of Ephesians 1, p. 49