Whenever I hear the words, "so and so was converted to Christianity" I cringe a little.
Conversion is not what God wanted, He wanted a transformation by His power in the life of those who believe on Him.
Often "converts" make their choice to be a Christian without a confession of their sinfulness, therefore they have not become born again by the Spirit of God.
These people learn all the cultural standards of those who attend church but are not dedicated to loving God or even His Word. They learn a few verses usually out of context and the rest of their philosophy is lived by cultural cliches that they think come from the Bible but that God never said.
We know their heart because when they are confronted with Biblical truth they fight to defend their sin and error. They "say" they are Bible believers but in reality, they are not.
Matthew 15:7-9 "…7 You hypocrites! Isaiah prophesied correctly about you: 8 ‘These people honor Me with their lips, but their hearts are far from Me. 9 They worship Me in vain; they teach as doctrine the precepts of men.’ ”