Zion is the place that the Lord has promised to reside with his Ark. The Ark of Covenant must be returned to Jerusalem and God will reside there (someday). David speak to not resting until He has found the Ark and brought it to its rightly home. He made God's business, his business. Do we ever put God's needs in front of our own? How selfish are we that we cannot place our Lord in front of ourselves? If you do not serve Him, then who do you serve?
Jerusalem continues to this day to be the most hotly contested physical location in the entire world. However, our God has declared it as the place for Him to reside. Verse 14 tells us so "This is My rest for ever: here will I dwell; for I have desired it." This continues a long list of promises yet to be fulfilled. However, the list of promises fulfilled grows every day as well. God will make true to this promise in the Kingdom Age and there will be nothing anyone can do to stop Him. Feel His almighty power when we recognize what our God is. Be thankful for every breathe as it may be our last. Only God knows our futures. What have you and God talked about? What things hath He promised you? Are you doing your side of the bargain to be "of God", rather than "of man"? What promises have we not kept? Self reflection in our faith journey is important. Do not let your sins eat away at you, you are forgiven! Instead, learn and move forward closer to God, just as David did.