The blood atonement of Jesus on the cross blots out our sin, as if we had never sinned. But we still have the Adamic nature. In water baptism, as we are totally immersed, our Adamic nature goes down to the grave, and we come up out of the water as a new creation, with our capacity to function in the spiritual realm restored.
"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." (Romans 6:4)
Now we can walk in "newness of life." Under the Law, righteous living was required, but man was incapable of this and utterly failed. In the New Covenant the ability to live a righteous life was given by the creative work of the Holy Spirit within our heart.
"A new heart also will I give you, and a new Spirit will I put within you: and I will take away the stony heart out of your flesh, and I will give you a heart of flesh. And I will put My Spirit within you, and cause you to walk in My statutes, and you will keep My judgments, and do them." (Ezekiel 36:26-27)
The Baptism in the Holy Spirit provides this "ability" that will "cause," or give us the "power" (Acts 1:8) that will enable us to live above sin as we become witnesses of “His Life”
(Acts 2:38) Then Peter said unto them, Repent, and be baptized every one of you in the name of Jesus Christ for the remission of sins, and ye shall receive the gift of the Holy Ghost.
The "blood" forgives our sin; the "water" changes our nature; and the "Spirit" gives us the ability (enabling power) to enter into the realms of the spiritual, above all that is earthly. These three together, as "one," provides a full salvation experience that will enable us to enter the Kingdom.