Through whom [Jesus Christ] we have received grace and apostleship to bring about the obedience of faith for the sake of his name among all the nations (Ro 1:5)
Now to him who is able to strengthen you according to my gospel and the preaching of Jesus Christ, according to the revelation of the mystery that was kept secret for long ages but has now been disclosed and through the prophetic writings has been made known to all nations, according to the command of the eternal God, to bring about the obedience of faith— to the only wise God be glory forevermore through Jesus Christ! Amen (Ro 16:25-27)
These verses come from the beginning and end of the book of Romans. Paul's great exposition of the gospel. At the start and at the end, like bookends, he lays out the purpose of his Apostolic ministry and of the gospel he preached: to bring about the obedience of faith.
I love that phrase. It encapsulates the inseparable nature of faith and obedience. One never leaves home without the other.
What is obedience without faith? Nothing, certainly not true obedience of the kind that pleases God. For without faith it is impossible to please him. It is just dry religious observance. A form of godliness but lacking its power.
And what is faith without obedience? Nothing, certainly not the faith of the kind that God responds to. It is just mental assent. A conviction of truth that does nothing to change our behaviour. James says even the demons have this kind of "faith" in God.
But faith married with obedience, what a team! The faith that does not just grip your thoughts, but moves your feet. A mustard seed's worth of this kind of faith can see the power of God released.
The faith that enabled Peter to walk on the water, was not a conviction that he would float (it is debatable how much of this kind of faith he had) but the determination that he would take that first step out of the boat. That step of obedience was the true manifestation of his faith, and the means of the miracle.