If salvation is of grace, by definition it is not contingent upon any effort of the one on whom it is bestowed. If there is subsequent effort to maintain salvation, by definition it no longer grace because it requires something of the individual.
Subsequent requirements may evidence the lack of grace to begin with, but can in no way be required if the transaction was truly grace alone.
In 1st John 2:24, it is written, if that which you have heard from the beginning shall remain in you, you also shall continue in the Son and in the Father.
And in John 15:10, Jesus said, if you keep my commandments, you will abide in my love, even as I have kept my father's commandments, and abide in his love.
If God has a requirement to abide in Christ and in his love, he also has a requirement to abide in his grace.
And how does one obtain this unmerited favor of God's grace? By faith and faith alone.
In Romans 11:20 through 22, Paul talks about how the Jews, being the natural branches, we're cut off from The Olive tree through unbelief, and we were grafted in through faith.
It goes on to say that if God didn't spare the natural branches because of their unbelief, he will not spare us through this same said unbelief.
Again, it shows a condition in order to remain or abide in either the vine or the tree, which is Christ.
So when the Bible talks about salvation being by grace it's not by works, it is referring to works of the flesh, not the work of believing in Christ and his finished work for your salvation.
If we are saved by grace through faith, then we are also healed by grace through faith, and delivered by grace through faith, and prayers answered by grace through faith.
Paul said, whatever is not done in faith, is sin, which brings damnation on yourself.
Again it is written, the only way, to please God, is by faith.
What did God tell Paul when he wanted deliverance from The Thorn in the flesh, which was the messenger of Satan?
He said, my grace is sufficient for you, for my strength is made perfect in weakness.
Was Paul in God's grace when he asked God to remove the devil for him? Absolutely not. Reason being, he used absolutely no faith to take care of the messenger.
No faith equals no Grace.
It should be understood then, that we can move in and out of the grace of God based on whether or not we are walking by faith in any given situation. For Grace is not for salvation alone but for every situation we go through.
And by the way, if we are not under grace, then we are, at that moment in Time, under the law. Which would constitute a work of the flesh.