Mark 1:4b 4: John did baptize in the wilderness, and preach the baptism of repentance for the remission of sins.
When we confess our sins and accept Jesus as our savior, we are washed by his grace and cover under the blood.
Isa. 1:18 18: Come now, and let us reason together, saith the LORD: though your sins be as scarlet, they shall be as white as snow; though they be red like crimson, they shall be as wool.
Act 22:16 16: And now why tarriest thou? arise, and be baptized, and wash away thy sins, calling on the name of the Lord.
Paul was given instructions of God to wash away his sins by baptism of the water, and by calling on the name of the Lord. The calling on the name of the Lord is the spiritual washing of sins. Water in itself is unable to wash away your sins. It is our faith/belief in Jesus as being our Lord and Savior; His blood was shed on the cross for many to wash away or cover our sins. Isa. 43:25 I, even I, am he that blotteth out thy transgressions for mine own sake, and will not remember thy sins.
When they stuck/pierced him in his side, water and blood ran out. John 19:34 But one of the soldiers with a spear pierced his side, and forthwith came there out blood and water.
This was and is symbolic of him bringing the Old and New Testament together. The Old Testament used symbolism through water for baptism to wash away men’s sin. In the New Testament, Jesus came and by way of the cross was crucified—even before he was crucified his blood was shed when he was torture and beaten. It was this, the shedding of his blood that cover our sins and was washed away. I John 1:7 But if we walk in the light, as he is in the light, we have fellowship one with another, and the blood of Jesus Christ his Son cleanseth us from all sin.
Today's baptism symbolizes us believing in Jesus Christ and him shedding his blood which washed away our sins. Baptism in water in itself does not guarantee our salvation nor does it makes us more holy. Believing in Jesus Christ is what guarantees our salvation. Just as communion is symbolic of his blood being shed and his flesh being torn on the cross. I Cor. 11:24&25.
We that take part in communion are acknowledging and believing in what Jesus Christ have done on the cross, so we take part in his suffering and crucifixion symbolically through communion. Communion in itself does not make us holy or more righteous but only remind us of why we believe and why we are saved. “Do this in remembrance of me.”