Is baptism just a symbol?

This is a consistent problem in modern Protestantism: differentiating the physical from the spiritual. That is actually Neoplatonism, the idea that anything physical is divorced from the spiritual realm, and it is not Christianity. The church fathers had deeply incarnational theology. When Christ says, if you eat of my body and drink of my blood, I abide in you and you abide in me, all early Christians saw this as a reality: a spiritual reality that happens in the world.

The Gospel of St John says the Logos, the divine rational principle of the universe, became flesh and dwelt among us. What was spiritual became physical, and the two were united. In the same way, when scripture says baptism is for the remission of sins, the earliest Christian understanding is that it is a physical event with intrinsic spiritual implications, and the two are not to be divorced.

In the book of Acts, the apostles meet people who have been baptized but have not received the Holy Spirit, and they anoint them and lay hands on them and they receive the Holy Spirit. Christ breathed on the apostles and they received the Holy Spirit. Everything that God does happens in this world. Reducing all of Christianity to belief in Jesus, where nothing else has any significance, is Protestant reductionism.

It does not align with the historical teaching of the church, which understood that real mystical events were encapsulated in real world events: the body and blood of Christ, baptism. It makes Christianity into an esoteric, borderline gnostic religion divorced from reality and anything physical.