Romans 6 is making the point that believing, repentant baptism changes the entire course of one’s life.
Our old self was crucified with Him in order that the body of sin might be brought to nothing, so that we would no longer be enslaved to sin. For one who has died has been set free from sin. Now if we have died with Christ, we believe that we will also live with Him. … So you also must consider yourselves dead to sin and alive to God in Christ Jesus. … Present yourselves to God as those who have been brought from death to life, and your members to God as instruments for righteousness (Romans 6:6-8, 11, 13).
Effective evangelism leads to faith that obeys in repentance and baptism. But biblical baptism is a beginning, not an end. It is the new birth of water and Spirit (John 3:5). What happens after a baby is born? It grows. Do we neglect it? Rather, we nurture and care for the baby. In the same way, we aim for spiritual newborns to grow and become “mature in Christ.”
Christ in you [is] the hope of glory. Him we proclaim, warning everyone and teaching everyone with all wisdom, that we may present everyone mature in Christ. For this I toil, struggling with all His energy that He powerfully works within me (Colossians 1:27-29).
Jesus makes a similar point about the “good soil” person. “He indeed bears fruit and yields, in one case a hundredfold, in another sixty, and in another thirty” (Matthew 13:23). On earth, this multiplying fruitfulness is the aim of effective evangelism. From the start, keep in mind this long-range goal: mature each person in Christ so that they reach and mature others.