Salvation is possible because of God's power in salvation. But that hardly means you don't have to secure that power through faith by your believing.
Even the faith to secure God's power in salvation is not of you, but that hardly means you do not then have to place your trust in Christ in response to the gift of faith. We know who has received that faith, not rejected it, and who are trusting God through that faith by if they are living for Jesus. Generally speaking, if they are still living in their old lives then we know they do not trust God for salvation.
We must continue to trust God through the gift of the power of faith to be saved when Jesus comes back. We know we are doing that and are ready to meet him at his coming by if we are living for him.
Morning! Regarding this issue and since you are in Romans, I would add what Paul also said:
You will say then, “Branches were broken off so that I could be grafted in.” That is correct: They were broken off because of unbelief, but you stand by faith. Do not be arrogant, but be afraid.
For if God did not spare the natural branches, He will not spare you either.
Paul was saying, don't boast against the natural branches, because they were broken off because of not having faith. And we as believers also stand by faith. Therefore, if we stop having faith, then we can be broken off as well. James 5:19 is pretty straight forward in regarding our salvation being dependent on continuing in faith:
"My brothers, if one of you should wander from the truth and someone should bring him back, consider this: Whoever turns a sinner from the error of his way will save his soul from death and cover over a multitude of sins."
Notice that James refers to them as "My brothers" demonstrating that they are believers. Then he mentions any of them who should wandering away from the truth and that while in that state they are accumulating sin and are on their way to death. But, if another believer warns them of their wandered state and they repent, then the multitude of sins that they will have been accumulating in that state are covered over and they are saved from death.
As the scripture states, "We are saved by grace through faith." But that faith is not a one time confession, but is required from beginning to end. Otherwise, what would be the purpose of all the warnings to believers throughout God's word if OSAS. If a person goes back into living according to the sinful nature, partying, sexual immorality, drugs, etc., then they have wandered from faith, which links them to God's grace. Paul makes this issue of continual faith pretty clear in the following scripture:
"Once you were alienated from God and were hostile in your minds because of your evil deeds. But now He has reconciled you by Christ’s physical body through death to present you holy, unblemished, and blameless in His presence—
if indeed you continue in your faith, established and firm, not moved from the hope of the gospel you heard, which has been proclaimed in all creation under heaven, and of which I, Paul, have become a servant.
The conclusion is that, salvation is obtained and maintained by remaining in faith from beginning to end.