"If anyone says that man can be justified before God by his own works, whether done by his own natural powers or through the teaching of the law, without divine grace through Jesus Christ, let him be anathema." (Council of Trent, canon 1)
The grace of God does not come about as a result of the doings of man (Romans 11:6). Simply put, to speak of grace being infused at the moment of water baptism (which is a work) and being maintained through good works is a contradiction of terms. Paul would have understood grace to be an unmerited favor of God.
In Roman Catholic theology, a person has to do good works in order to get justified in the sight of God. One keeps their right standing before Him by that same means. Rome teaches that one must attain an inherent righteousness in order to be accepted by God. However, that line of thinking runs contrary to Scripture.
We have failed to meet the standard of moral perfection that God requires and so incurred condemnation (Psalm 14:2-3; Isaiah 64:6; Romans 3:9-23; Galatians 3:10). If He kept a record of the sins of mankind and chose not to be merciful toward us, none of us could stand (Psalm 130:3). We do not look to ourselves for righteousness but to Christ alone (Luke 18:9-14; Philippians 3:3-9).
The point of contention is not whether our walk with God is to be characterized with a desire to serve Him. Our good works are a display of His grace in our lives. However, they are not to be viewed as meritorious in His sight. Our grounds for justification before God is the shed blood of Jesus Christ alone (Romans 5:19).
If justification is "not of ourselves" and "not as a result of works" (Ephesians 2:8-9), then that means faith alone is the instrumental cause of justification before God. Justification is not obtained by both grace and works because it cannot be done that way. There are no good deeds that can save us from eternal condemnation, including those done in a state of grace.
Elsewhere, the Apostle Paul says, "He saved us, not on the basis of deeds which we did in righteousness..." (Titus 3:5). He continues on that thought with a stark contrast, "but according to his mercy he saved us." Thus, Paul would most definitely have condemned the sacramental system of justification taught by the Church of Rome.