Why catechumens would spit symbolically on Satan before being baptized

In the early Church, this act of renunciation was much more prominent and included several physical acts.

According to the Catholic Encyclopedia, this included facing West and spitting at Satan.

Sometimes this would include spitting on particular idols that the catechumen formerly worshiped.

St. Cyril of Jerusalem adds a few more details of this ceremony before baptism.

This is an important aspect of Baptism, as it severs any tie one might have to Satan, pledging instead to worship Jesus and be at his service.

St. Cyril explains that the catechumen would then turn to the East, accepting the light of Christ.

While the current rite of Baptism isn't as physical in the act of renunciation, it still remains a powerful ceremony, one that is repeated every Easter Vigil, when everyone present professes the words of renunciation anew.