Following is an argument that is directly relevant to the matter at issue. I suggest this argument demonstrates that it is simply unBiblical to see baptism as an event which "symbolizes" or "signifies" our past repentance. To the extent that this argument succeeds, it overturns one of the primary objections to infant baptism, namely the notion that one needs to understand and repent prior to baptism. Here is the argument:
The "repent and only then be baptized" position cannot be squared with the teaching of Paul in Romans. In Romans 6, he asserts that baptism enacts a death - the death of the old nature, a nature that needs to be put to death so that the new life can take its place:
We died to sin; how can we live in it any longer? 3Or don't you know that all of us who were baptized into Christ Jesus were baptized into his death? 4We were therefore buried with him through baptism into death in order that, just as Christ was raised from the dead through the glory of the Father, we too may live a new life
For Jesus, the sequence was death on the cross and then resurrection to new life. Paul clearly has us dying in the act of baptism. Now to the extent that we understand repentence to be constitutive of the new life, it makes absolutely no sense to promote a model whereby we undertake the restorative journey of repentance and then enact our own death through baptism. That would have us putting our repentant "new nature" to death!
If we are following Paul's line of thinking, we understand the act of baptism as our sharing in Jesus' death (as we go down into the water) and emerging, like Christ, out the other side (as we are raised up out of the water). It is only after we have put the old self to death can we begin the process of repentance:
The mind of sinful man is death, but the mind controlled by the Spirit is life and peace; 7the sinful mind is hostile to God. It does not submit to God's law, nor can it do so.
Now to drive the point home yet again. We know Paul likens baptism to our death. Who is dying? The old Adamic nature, of course! What does Paul say about the old Adamic nature? That is cannot submit to God. That is, it cannot repent.
Unless and until you have put the Adamic identity to death in baptism, you simply do not have capability to repent.
Another way to understand the incoherence of the “repent and only then be baptised†position is to think of the “new creation†model that Paul gives us – if any man is “in Christâ€, he is a new creation. So assuming that we all agree that repentance is part of the expression of that new creation, it hardly makes sense to undertake repentance and then have that new creation be put to death - Paul is quite clear that baptism enacts our death.
Now, of course, this is not a positive argument for infant baptism - it merely shows that one need not, in fact one cannot, be baptized in order to symbolize a past act of repentance. And this belief that baptism symbolizes a "change of life" is one of the primary pillars on which rests the belief that infant baptism is not scriptural.