Paul says in Romans, chapter five, that we are justified by faith (v. 1). Faith means trusting God to love us, because of what he did in Jesus Christ, and entrusting ourselves wholeheartedly to that divine love. Salvation is by grace — we do not deserve God’s favor toward us and we can never earn it. We access this grace by faith, which means that we must always look outside ourselves for our salvation (2 Tim. 1:12).
We cannot perform the work which results in our salvation, for Jesus has already done that, once for all time. We cannot add to that finished work, or improve on it. We can only trust God to be gracious to us as he promises in Christ. If we picture grace as the room of God’s favor, we may think of faith as the door into that room (Rom. 5:1-2).
God accepts us because of Christ’s work on our behalf. We enjoy that grace by accepting it as fact, trusting it as sufficient, and throwing ourselves on it in total and eternal abandon, to become servants of righteousness and true holiness in Christ. We do not earn God’s favor. We can not ever please Him enough to be given His blessings. We certainly could never pay for our own sins and be saved. But in Christ God has brought together the justice that is his nature and the weakness that is ours: Christ became a man and took our place.
God’s grace deals with the weakness of our flesh because salvation does not depend on our weak flesh — Jesus has earned it for us already! It also takes into account God’s holiness, because sin is punished — by the death of God’s sinless Son! And so Paul can say to the Ephesians’ Christians:
For by grace you have been saved through faith, and that not of yourselves; it is the gift of God; not as a result of works, that no one should boast (Eph. 2:8-9).