Hi William,
I wrote:-
'It is fitting only to baptize true disciples......We do our best to achieve [this] by baptizing only those who make a credible profession of faith.'

You asked for scriptural proof.

I offered Mark 1:4-5; Matt 28:19; Acts 2:38-9 & 8:37.

If I understand you correctly, you are now asking for exposition on these texts.

In Mark 1, we read that John's baptism was one of repentance; and those who were baptized by him made a confession of their sins. Indeed, in Luke 3:8, John demands not only repentance, but evidence thereof, in other words, 'a credible profession'. Now Christian baptism is not identical to that of John, but their ministry at this early stage was the same- that of repentance (Matt 3:2; 4:17). Therefore we learn that repentance of sin is a pre-requisite for baptism.

In Matt 28:19, our Lord told His apostles to make disciples* and baptize them. Therefore it is disciples whom we are to baptize. Put the two texts together and we have repentant disciples. These and these alone are the proper subjects for baptism.
*[ The KJV translation of 'matheteusate' as 'teach' is poor. The NIV, NKJV, ESV and NASB all give the correct rendering, 'Make disciples'. Mathetes = Disciple]

So how does this work out in practice? In Acts 2, Peter preaches the Gospel on the Day of Pentecost. Many of his listeners are brought to a state of conviction (v37). Peter tells them to repent and be baptized (v38). In v41, we are told that 'those who gladly received his word were baptized.' We may suppose from this that there were those who rejected his word; they were not baptized. The apostles did not baptize willy-nilly; they distinguished between those who 'gladly received' the Gospel, and those who didn't. We are not told that the believers brought their children with them. If there were children present, then they were old enough to believe Peter's Gospel and to repent.

Finally, Acts 8:36-7. '...And the eunuch said, "See, here is water. What hinders me from being baptized?" Then Philip said, "If you believe with all your heart you may," And he answered and said, "I believe that Jesus Christ is the Son of God."' [I'm aware that the majority of Greek texts do not have Acts 8:37, but even if it is an interpolation, surely some similar conversation must have taken place?]

The eunuch, having heard the Gospel from Philip, asked to be baptized. Philip asked for, and received, a clear confession of faith from him. Surely it is a good and reasonable inference that if Philip had regarded the eunuch's confession as not credible, he would not have baptized him.

So there you are! The Bible clearly requires repentance and faith as pre-requisites for baptism. We see that John asked for 'fruits worthy of repentance', that the apostles only baptized those who 'gladly received' Peter's word, and that Philip required a clear and credible statement of faith from the eunuch.

Case made?

Every blessing,

Itinerant Preacher & Bible Teacher in Merrie England.
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