I would like to know, is it really important for a grown person to be baptized? If you feel like you are renewing your inner spirit man and reading the Bible and spending alone time with God, then isn't that enough? It's the same as what Paul describes circumcision and uncircumcision. Why is it important to be baptized in water?
"And in Him you were also circumcised with a circumcision made without hands, in the removal of the body of the flesh by the circumcision of Christ; having been buried with Him in baptism, in which you were also raised up with Him through faith in the working of God, who raised Him from the dead. When you were dead in your transgressions and the uncircumcision of your flesh, He made you alive together with Him, having forgiven us all our transgressions" (Colossians 2:11-13).
Baptism carries some similarities to circumcision. Both involve a cutting away of something. Physical circumcision involved removing a section of the foreskin -- a physical removal of flesh. Baptism also involves a removal but it is not physical but spiritual. It removes sins -- "the body of the flesh." See The Works of the Flesh for more details.
The same thing is said by Paul in "Or do you not know that all of us who have been baptized into Christ Jesus have been baptized into His death? Therefore we have been buried with Him through baptism into death, so that as Christ was raised from the dead through the glory of the Father, so we too might walk in newness of life. For if we have become united with Him in the likeness of His death, certainly we shall also be in the likeness of His resurrection, knowing this, that our old self was crucified with Him, in order that our body of sin might be done away with, so that we would no longer be slaves to sin; for he who has died is freed from sin" (Romans 6:3-7).
Physical circumcision is no longer necessary because it was a sign of the old covenant. "For in Christ Jesus neither circumcision nor uncircumcision means anything, but faith working through love" (Galatians 5:6). The Old Law is no longer in effect so the sign of being under the Old Law is no longer necessary.
However, baptism remains necessary if you wish to be forgiven of your sins. You might feel that you are following Christ, but until you obey Christ your feelings are misleading. "Why do you call Me, 'Lord, Lord,' and do not do what I say? Everyone who comes to Me and hears My words and acts on them, I will show you whom he is like: he is like a man building a house, who dug deep and laid a foundation on the rock; and when a flood occurred, the torrent burst against that house and could not shake it, because it had been well built. But the one who has heard and has not acted accordingly, is like a man who built a house on the ground without any foundation; and the torrent burst against it and immediately it collapsed, and the ruin of that house was great" (Luke 6:46-49). See Why Were They Baptized so Soon?