Follow-up increases the effectiveness of a previous decision or action made, by building on, continuing and reinforcing it.
A vital aspect of evangelism
teach, and travailing in prayer for them that they will be transformed by Christ (Gal 4:19; Col 4:12; 2 Tim 1:3,4). It will soon become evident if a person ‘making a decision’ was genuinely convicted of their sin by the Holy Spirit and they were genuinely converted or if they just responded emotionally and will soon fall away when spiritual attacks come.
Jesus said, “make disciples, by teaching them…” (Mt 28:19,20). Jesus instructed His disciples, and it was a requirement of those in church leadership to be capable of passing on sound doctrine as contained in the Bible (Mt 11:1; 2 Tim 3:16; Tit 1:9). It is not just getting converts and letting them flounder, rather it requires instructing them in the basics of the Christian faith and being a support to them while they become established, and knitted into a church family (Act 11:26).
Paul revisited the converts made on his first missionary trip, then later when he was unable to make another visit Timothy was sent to teach and establish them (Act 15:36; 1 Thes 3:1,2).