"If I forget you, O Jerusalem,
let my right hand forget its skill!
Let my tongue stick to the roof of my mouth,
if I do not remember you,
if I do not set Jerusalem
above my highest joy!"
Here's some context. This psalm was written as a response to God's people, Israel, after being deported and exiled into Babylonian captivity (586-539 B.C. if you were curious). The Babylonian conquest was a discipline delivered by God in response to his people's lack of trust and proper worship of him in the decades prior. So the psalmist is pretty much mourning over this period, and is repenting of "forgetting God." You see, at the time (before the Christ) Jerusalem and her temple were considered the center of Jewish worship. To truly worship God, one must be in his presence at the temple. Therefore, the writer of the psalm is associating communion and worship of God directly with Jerusalem, and rightfully so.
It's Old Testament, but the principle completely applies to Christians today. When Jesus died and rose from the grave, he did away with the former way of worship.
"The hour is coming when neither on this mountain nor in Jerusalem will you worship the Father..." (John 4:21).
"The hour is coming, and is now here, when the true worshipers will worship the Father in spirit and truth..." (John 4:23).
The point Jesus was making in this passage is that the worship of God will no longer be done in one location, but can be done wherever a believer is present. Whoever has been born again, the spirit of Christ dwells in them, so communion and fellowship with God is constant. We have become the holy Temple, the dwelling place of the living God (Romans 8:11)!
So if I understand the above verses as the psalmist understood them, I might say something like, "If I forget to worship(!), if I forget to spend time with you(!), if I forget to acknowledge you everyday(!), then render me useless! Without you, I am unskilled and ineffective. Nothing I have to say is worth anything!"
My efforts then, in my own strength, are just chasing after wind. I must not forget my Lord, because he is actually the one who does any good in and through me anyway (Philippians 2:13). I have to make him my priority (above my highest joy!), or I will be useless for kingdom work. I must come to my "Jerusalem" and live by his grace, for it is full, sufficient, and effective.
