You mean that if allele frequencies change over time, then Jesus didn't die on the Cross? I don't profess to be an expert in Christian theology (it's not my religion, first of all), but I'm not sure I follow your reasoning.
No, what I am meant was, if man descended from earlier primates, rather than was “made from scratch” in the Garden of Eden, Genesis is repudiated, and specifically the doctrine of “original sin” resulting from Adam’s fall from grace is repudiated. And if original sin is repudiated, Jesus’s death and resurrection were unnecessary. The Christian faith is based on the notion that God sent Jesus to earth as savior, i.e. to redeem man for his original sin (Adam’s), and as the exclusive pathway to redemption.
Therefore, one cannot believe in both evolution (macro, not micro) and Christianity. The creationists have a lot at stake in taking on evolution, for if they are wrong (as they surely are), their entire religion is nonsense.