How can one justify being a Christian if he claims to believe but is not baptized until some time later? Is he convinced that baptism does not save you?
Many denominations teach people that belief is all that is required for salvation. Some, such as the Baptists, do practice a form of baptism, but they claim that its sole purpose is to make you a member of their denomination. According to their teaching, baptism has nothing to do with salvation, but it is just "an outward sign of an inward grace." Many of the charismatic denominations redefine baptism from immersion in water to immersion in the Spirit. They also believe that baptism is not required for salvation, but they see two levels of salvation: those who believe are saved, but those who are baptized in the Spirit are sanctified. All of these practices are based on using selective verses from the New Testament.
You did hit upon the core of the problem. They don't really believe what God said. Instead of accepting verses, such as:
"He who believes and is baptized will be saved; but he who does not believe will be condemned" (Mark 16:16).
"Then Peter said to them, "Repent, and let every one of you be baptized in the name of Jesus Christ for the remission of sins; and you shall receive the gift of the Holy Spirit" (Acts 2:38).
"And now why are you waiting? Arise and be baptized, and wash away your sins, calling on the name of the Lord" (Acts 22:16).
"Corresponding to that, baptism now saves you--not the removal of dirt from the flesh, but an appeal to God for a good conscience--through the resurrection of Jesus Christ" (I Peter 3:21).
They search for ways to explain how these verses don't really say what they are obviously saying. Therefore, they don't believe what God said or don't believe that God was able to express Himself clearly on this matter. They claim the name of a follower of Christ, but as Christ Himself said, "But why do you call Me 'Lord, Lord,' and do not do the things which I say?" (Luke 6:46). And in another place, He 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. Many will say to Me in that day, 'Lord, Lord, have we not prophesied in Your name, cast out demons in Your name, and done many wonders in Your name?' And then I will declare to them, 'I never knew you; depart from Me, you who practice lawlessness!'" (Matthew 7:21-23).