The Holy Spirit [through His Word], and the water [through His immersion] and the blood [through His crucifixion]; and these three agree together [in giving testimony about Him].
This water prefigured immersion [into Christ], which now also saves you, not by removing dirt from the [physical] body, but [by serving] as an appeal [or, “pledge”] to God for a clear conscience through the raising of Jesus Christ from the dead.
So, as you go, make disciples out of people from all the nations, then immerse believers [See Mark 16:15-16] into the name of [i.e., to enter a relationship with] the Father, and the Son and the Holy Spirit.
For it is impossible to get people who were once enlightened [by the Gospel message], and who had experienced the gift from heaven [i.e., forgiveness, never ending life, etc. See Rom. 6:23], and who had partaken of the [indwelling] Holy Spirit [See Acts 2:38],
If we [are willing to] accept the testimony of people about matters, [surely we ought to accept that] the testimony of God is more reliable; because the testimony of God is that He has presented [confirming] testimony concerning [the identity and mission of] His Son.