Believing in Christ is not just intellectually agreeing that He is Lord and Savior. Jesus said, “Not everyone who says to Me, ‘Lord, Lord,’ shall enter the kingdom of heaven, but he who does the will of My Father in heaven” (Mt 7:21). True faith involves obeying the Lord’s words about salvation (Lk 6:46-49).
We are saved by grace through faith, but faith without deeds is not true faith (Jas 2:14-20). Even evil spirits believe that Jesus is the Son of God (Mt 8:28-29; Lk 4:41), but their belief is not true faith (Jas 2:19-20).
We need to follow what Jesus says to be saved. For example, regarding baptism He said, “He who believes and is baptized will be saved; but he who does not believe will be condemned” (Mk 16:16). We cannot dismiss the necessity of baptism since baptism itself is an act of belief and faith in Jesus Christ (see Acts 16:30-33).
Trying to do good is an admirable quality. But without God, no matter how hard we try, we can never be perfectly good because of sin in our nature and in our lives (see Rom 3:23). Trying to do good is just not good enough, because we can never save ourselves from sin (Rom 3:20).
Just because you are sincere, doesn’t mean you are right. Sincerity in religious matters is not good enough, just as it is insufficient in other situations: “Is it sufficient that your surgeon, your accountant or your travel agent be sincere? Is sincerity alone enough to save you from cancer, bankruptcy, accident or death? It is not. Why then do you think it should be enough to save you from hell?” (Peter Kreeft and Ronald Tacelli, Handbook of Christian Apologetics [Downers Grove, IL: InterVarsity Press, 1994], 323).
The only way we can fulfill God’s righteous standards is to rely on God. He has provided us salvation from sin through the sacrifice of Jesus Christ. The only way we can be saved is through faith in Jesus Christ, for He alone can deliver us from sin and judgment (Eph 2:8-9). This is not by our works of righteousness, but according to His mercy (Titus 3:5).