If we are saved by grace, why don't we just go out and sin? This is an objection often made to the teaching of salvation by grace through faith. How do we deal with this?
The first thing we should note as a preliminary is that saving faith must be a sincere faith. God knows the heart and is not going to be fooled by outward appearances (1 Samuel 16:7; Matthew 6:6; Romans 2:16; 1 Timothy 5:24,25). This answers another related question, of whether I believe in deathbed repentance. My answer is, yes I do (Luke 23:39-43), but it has to be a sincere repentance. The person who decides to live in sin with the idea they can repent on their deathbed will not, barring a total change of heart that includes repudiating their original choice, be able to sincerely repent.
If, then, a person has a sincere faith it will have certain results. They will recognize they are a sinner (Romans 3:23) and were in danger of eternal punishment (Romans 6:23). Involved in this is the idea that God is the One who should be obeyed and that not obeying Him has negative consequences (Galatians 6:7,8). Are we, then, to conclude we should go back to the thing that was wrong and that nearly destroyed us (Romans 6:21,22)? Also, if we have genuine faith we will recognize that God paid an incredible price to deliver us from the punishment we deserved (John 3:16; Romans 5:8). Our logical response should be love of God ( 1 John 4:19; 2 Corinthians 5:14,15), which results in obedience to His commandments (John 14:21; 1 John 5:2). How far this will go in any individual's life will depend on their choices, but genuine faith should produce results (James 2:20; 2 Peter 1:9). Could one of the reasons we do not see as much of a result as we would like in the lives of professing Christians be failure to teach clearly the content of the gospel?
Also, when a person comes to Christ, the Holy Spirit comes into their life to work to change it (2 Corinthians 3:18; Romans 8:9; Philippians 2:13) and begins to work through them to minister to others (Ephesians 2:10; Colossians 1:29; 2 Corinthians 3:5,6). Again, how far this working will go in a particular individual depends on their response to it (Galatians 5:16; Ephesians 5:18; Philippians 3:12-14), but we should expect an effect in their lives.
I would therefore conclude that the result of salvation by grace is a changed life (Titus 2:11,12) and that the logical response to it is to present ourselves to God to carry out His purposes (Romans 12:1,2: 6:12-14). We should be careful of judging others, though (Romans 2:1,2; Matthew 7:1-5), but should correct others with gentleness (Galatians 6:1; 2 Timothy 2:24-26). And remember the case of Lot, whose soul was tormented over the deeds done in Sodom (2 Peter 2:6-8), and who despite appearances was a saved man.