What makes people do what they do? In this passage, Paul says he is compelled by the Holy Spirit.
We are moved by hunger, desire, ambition, greed, need, love or lust (they are not the same thing), or any number of other motivations. But the Christian is moved, or should be moved, by the Holy Spirit alone.
The first desire is, or should be, to please God. In order to do this, we need to know what He wants of us. He has told us very specifically in His word. Love Him and love one another.
Love is not just a feeling, it manifests in action. Those actions are led by the Holy Spirit if one is a Christian. It is the Holy Spirit that leads us into all truth. The Holy Spirit is our guide, our interpreter of God's will. Our spirits are connected to the Holy Spirit by the grace of God.
This is the Comforter of whom Jesus spoke. When one is convinced by the Holy Spirit of a specific course of action, he will not be dissuaded from it.
The brethren entreating Paul not to return to Jerusalem always reminds me of Peter when he told Jesus they would not allow Him to be taken and crucified. The will of God is the essence of the Holy Spirit. When we voluntarily surrender our free will to the will of God, nothing can change us just as nothing can change Him.
Paul was unmoved from his decision to return to Jerusalem. His steadfast purpose finally convinced those who would have persuaded him otherwise to simply resign themselves to God's will -- which is where they should have been in the first place.
Grant us the wisdom to seek Your will in all our endeavors. Your plans are perfect. Keep us steadily on the path You would have us travel.
In Jesus' most precious name.