Why shouldn't we expect new believers to be as mature as older Christians?
New believers begin as spiritual infants, just as physical life starts with babies who must grow. The spiritual life parallels the physical, and no one is born into God’s family fully mature. They come as babes in Christ, so failures and gradual growth are expected. All grace is given at salvation, but maturity develops over time.
Les teaches that the spiritual life is a parallel with the physical. You do not get born into the family of God a full, mature spiritual person; everyone comes into salvation as babes in Christ. He illustrates this with an old evangelist who traveled by train and could tell which homes had babies because diapers hung on the clothesline, since there were no washers and dryers. It is the same spiritually: all had to begin as babes in Christ, and consequently there will be failures. No infant comes into the world trained to go to the bathroom, and so it is with infant believers. We cannot expect them suddenly to be mature or to have the same spiritual discoveries that longer and older Christians have. The Corinthians were saved out of abject paganism, idolatry, and immorality, so there had to be a time of nurturing and growth, but only by the grace of God. Every saved person experiences all of God’s grace at salvation, yet there is a long way to go in growth. Peter says to grow in grace; we do not grow into grace. All of God’s grace is poured out the moment we believe, and from that position in grace we grow. Grace is not law, so nothing is forced upon us.