Pierre Marcel makes a good point here about the focus of the Apostles when they discuss baptism.

It is significant that all the principal texts referring to baptism in the Epistles were not written with a view to informing us of the conditions necessary for admission to it, but with the purpose of describing the fruits which ought to follow for those who have already received it,  and to define the ends to which it should conduct those who are careful to preserve the memory of the baptism they have received.

Here is the Westminster Larger Catechism on how Christians should improve their baptisms:

Q167: How is our Baptism to be improved by us?
A167: The needful but much neglected duty of improving our Baptism, is to be performed by us all our life long, especially in the time of temptation, and when we are present at the administration of it to others;

• by serious and thankful consideration of the nature of it, and of the ends for which Christ instituted it, the privileges and benefits conferred and sealed thereby, and our solemn vow made therein
• by being humbled for our sinful defilement, our falling short of, and walking contrary to, the grace of baptism, and our engagements
• by growing up to assurance of pardon of sin, and of all other blessings sealed to us in that sacrament;
• by drawing strength from the death and resurrection of Christ, into whom we are baptized, for the mortifying of sin, and quickening of grace;
• and by endeavoring to live by faith, to have our conversation in holiness and righteousness, as those that have therein given up their names to Christ; and to walk in brotherly love, as being baptized by the same Spirit into one body.

Finally here is the Second Helvetic Confession on the obligation which baptism places upon us:

THE OBLIGATION OF BAPTISM. Moreover, God also separates us from all strange religions and peoples by the symbol of baptism, and consecrates us to himself as his property. We, therefore, confess our faith when we are baptized, and obligate ourselves to God for obedience, mortification of the flesh, and newness of life. Hence, we are enlisted in the holy military service of Christ that all our life long we should fight against the world, Satan, and our own flesh. Moreover, we are baptized into one body of the Church, that with all members of the Church we might beautifully concur in the one religion and in mutual services.

We tend to focus on regeneration and baptism or justification and baptism. But in the Bible, especially the Epistles, baptism is about our sanctification.