Imagine that.
It's the blood that cleanses us from sin, not the washing of dirt from the body.
Sin is an internal heart issue, not an external, physical body issue. Getting the skin on the body wet does not cleanse the soul from the guilt of sin.
Jesus Himself said that His blood was necessary for the forgiveness of sin.
Matthew 26:27-29 27And he took a cup, and when he had given thanks he gave it to them, saying, "Drink of it, all of you, 28for this is my blood of the covenant, which is poured out for many for the forgiveness of sins.
Hebrews 9:22 Indeed, under the law almost everything is purified with blood, and without the shedding of blood there is no forgiveness of sins.
1 John 1:7 But if we walk in the light, as he is in the light, we have fellowship with one another, and the blood of Jesus his Son cleanses us from all sin.
Revelation 7:13-14 13Then one of the elders addressed me, saying, "Who are these, clothed in white robes, and from where have they come?" 14I said to him, "Sir, you know." And he said to me, "These are the ones coming out of the great tribulation. They have washed their robes and made them white in the blood of the Lamb.
If washing the body could gain the forgiveness of sin, then Jesus died for nothing.
Romans 6:4 Therefore we are buried with him by baptism into death: that like as Christ was raised up from the dead by the glory of the Father, even so we also should walk in newness of life. 5 For if we have been planted together in the likeness of his death, we shall be also in the likeness of his resurrection:
Matthew 26:28 For this is my blood of the new testament, which is shed for many for the remission of sins.
Baptism just like the Protestant communion are a spiritual exercises. It is not the water that cleanses any more then the bread and wine physically become the body and blood of Jesus. They are in both cases the spiritual equivalent of being cleansed by the blood and partaking of the flesh and blood of Christ.
Do we need to be baptized? Yes, its a spiritual exercise of being cleansed by the blood. We walk in the spirit not in the flesh.