Psalm 52 is a study in contrasts. It begins looking at the evil person (as summarized in v. 7) and ends looking at the faithful, godly one. The boasts of the two are contrasted, as is their desire, their faith, and the reaction they get from God. A remarkable feature of the godly one is that he gets to hang out in the presence of God with other godly ones and worship. Worship as fellowship, imagine that!
Worship is fellowship with God
The faithful one is cast as a green olive tree in the house of God. That would seem a rather passive symbol, but there's much to recommend it. It is green, which means it is full of vitality. It is a tree, so its place is its place of abiding--trees don't come and go--it dwells in God's presence. It is an olive tree which means its fruitfulness provides oil which produces both sustenance and light.
An olive tree planted in the Temple grounds is in the happy situation of dwelling in the light of God. There it flourishes as a result of hanging out in the presence of God. It has abundant life flowing within and productive life blossoming and ripening without. It is alive as live can be, resting in the lovingkindness of God, but is there any action?
Yes, there is--praising. "I will give you thanks" (as in the NASB above) would probably be bettered rendered as "I will praise you" (as in the NIV). The Hebrew word underlying the English translation comes from a root which means "casting" or "throwing" and which came to be used figuratively of the act of praising. In worship we cast our thanks, we cast our wonder, and we cast our submission to or upon God.
When the faithful one is fellowshipping with God, planted like a tree in his presence, that one showers God with love and gratitude. Not a surprising response, given the wonder of who God is, it could hardly be helped. To fellowship with God is to break out in praise. Maybe we could jump to the conclusion and say by extension: to truly worship is to fellowship with God.
Worship is fellowship with God's people
That green tree planted in the temple of God is not alone. Others are present as well, godly people looking to God. Praise can be done alone, but is not something reserved for solitude. As for the individual, so too for the group: faithful people in the presence of God can hardly keep from breaking forth in praise. To truly worship in congress is to fellowship with God and man.
I think our fellowship with one another is missing something without genuine worship being part of our shared experience. Not all of our fellowship has to be centered around worship, but it is a dynamic that is healthy for us as individuals and as a body. Together, we are the temple of God. Worship is our fellowship.