Joseph Ng, elder son of my church's late founding pastor came up with four stages of preaching the good news. Instead of the "God loves you and have a wonderful plan for you" stuff as the beginning, he replaced it with the introduction of the creator God and his coming judgement.
Stage 1
Then I saw another angel flying in mid air, and he had the eternal gospel to proclaim to those who live on the earth - to every nation, tribe, language and people. He said in a loud voice, "Fear God and give him glory, because the hour of his judgment has come. Worship him who made the heavens, the earth, the sea and the springs of water." (Revelation 14:6-7 NIV)
For he has set a day when he will judge the world with justice by the man he has appointed. He has given proof of this to everyone by raising him from the dead." (Acts 17:31 NIV)
You frightened the unbeliever sufficiently with God and judgement until he cried out, "What must I do to be saved?"
Sign of change:
Fear. Human growth equivalent - none that I can think of.
Stage 2
They replied, "Believe in the Lord Jesus, and you will be saved - you and your household." (Acts 16:31 NIV)
At that hour of the night the jailer took them and washed their wounds; then immediately he and all his household were baptized. (Acts 16:33 NIV)
You say, "Believe in the Lord Jesus and you will be saved." and he replied, "I believe!" and you get him baptized.
Sign of change:
Baptism. Human growth equivalent - birth of a baby.
Stage 3
Therefore let us move beyond the elementary teachings about Christ and be taken forward to maturity, not laying again the foundation of repentance from acts that lead to death, and of faith in God, instruction about cleansing rites, the laying on of hands, the resurrection of the dead, and eternal judgment. (Hebrews 6:1-2 NIV)
You are to abstain from food sacrificed to idols, from blood, from the meat of strangled animals and from sexual immorality. You will do well to avoid these things. Farewell. (Acts 15:29 NIV)
You feed him with 6-point milk and 4-don't porridge until he matures.
Sign of change:
No single significant moment. Human growth equivalent - reach puberty, voice change, grow hair, grow big.
Stage 4
A fully grown adult.
Others
These are some other things I wrote in this blog on Christian Living:
Bringing Up the New Man
Do
What Every Christian Must Do - 1 Overview
What Every Christian Must Do - 2 Read
What Every Christian Must Do - 3 Pray
What Every Christian Must Do - 4 Grow
What Change When One Becomes A Christian
How Should Christians Live
Christian Living Summary For April 2019