Hi Seattlegal —
So it is different from the baptism John the Baptist and Jesus's disciples performed.
I would rather say theology has illuminated aspects of the Rite that were not immediately visible, but are nevertheless implicit.
Christian baptism is not purely the washing away of sin — it's an infusion of Divine Grace which actualises the possibility of a personal communion with the Divine that exists potentially within human nature — that's more than simply the forgiveness of sin.
Catholicism holds that human nature is 'deiform', that man was made to know God subjectively and not just objectively, but that the Divine Subjectivity — the sense of interior presence — was withdrawn in the face of the offence of the Fall.
It is this subjective knowing — Divine Immanence — which was lost. Objective knowing remained, as is obvious from the religious aspirations of man throughout history.
Repentance of itself is prior to and a prerequisite of baptism, in the same way that repentance is prior to confession (if one does not repent in one's heart, then the Sacrament is void — it's not a magical ritual). So baptism doesn't
enable one to repent, it's a sign of a prior desire for repentance, and a sign of acceptance of repentance.
As the ontology of sin is an offence against God, repentance does not necessitate forgiveness, as you can offend your neighbour, apologise, but he is not required to accept your apology, to forgive and forget. That God always forgives is by virtue of the infinity of His mercy but it's not something we should take for granted.
As an act of repentance it assumes the axiom of faith that the Holy Spirit will come to the assistance of those who seek the life in Christ. So it performs two things: One is the washing away of sin ('ancestral sin' as the Orthodox call it), the forgiveness of the offence and allowing the person to continue with a 'clean sheet', as it were.
Implicit in the Christian community is the idea that in the forgiveness of sin the Father then 'opens communications' in and with the soul at the level of person — Divine Subjectivity — the Sermon of the Vine, for example, indeed the whole thrust of Our Lord's discourse at the Last Supper, and the Mystical Body of which St Paul teaches.
Baptism in the Catholic sense is not just the washing away of the ancestral stain, but by so doing the incorporation into that Mystical Body.
Thomas