Baptists like to point to the word “conscience” in 1 Peter 3:21, saying that if baptism is “the answer of a good conscience toward God”, then it must be something that only sentient adults can do.
This is, however, an anachronistic retrojection of the English meaning of “conscience”, which means something like “awareness of one’s own ethical behavior.” But the Greek word is broader, encompassing “acknowledgement” or “judicial admission of guilt”.
It is used in Hebrews 10:22 “Let us draw near with a true heart in full assurance of faith, having our hearts sprinkled from an evil conscience, and our bodies washed with pure water.”
From a baptist perspective, the phrasing of this verse is odd. How could sprinkling — water baptism, obviously — remove an evil conscience? A baptist might try to say that Hebrews is speaking metaphorically or metonymically. Yet the following clause, “our bodies washed with pure water” is obviously a literal description of the ritual of baptism.
I need to do more work on this word “suneidêsis”, but at the moment, the most plausible way to take it is as one’s “slate.” With what record do we stand before God? A clean one, or one loaded with sins? Or one that is defiled, with an awareness of guilt?
Romans 2:15 speaks of the Gentiles’ consciences being witness, excusing or accusing.
When Paul speaks of his conduct as a steward of God, he says, “But with me it is a very small thing that I should be judged of you, or of man’s judgment: yea, I judge not mine own self. For I know nothing (ouden sunoida — the direct verbal cognate of suneidesis) against myself; yet am I not hereby justified: but he that judgeth me is the Lord.” He is speaking here of his judicial innocence, and says that he has no suneidesis of anything.
Hebrews says that the sacrifices of the Torah were unable to “make him that did the service perfect as pertaining to his suneidesis” (Heb. 9:9), and that “the blood of Christ… shall purge your sundeidesis from dead works (9:14). If the Mosaic sacrifices had been able to finally eliminate sin, then “the worshippers once purged should have had no more suneidesis of sins” (10:2).
It seems very obvious that suneidesis does not mean, in these passages, subjective awareness or personal feelings of guilt over sin. The mere absence of such feelings could just as easily be the mark of a sociopath as of an innocent man. Nor was the aim of the Mosaic sacrifices to change the feelings of the offerer. Rather, they were aimed at changing his standing before God. The meaning is objective: what is on your record?
So in connection with Baptism and 1 Peter 3:21, we can say that baptism is when one is born again and formally united to Christ: “as many of you as have been baptized into Christ have put on Christ.” With Christ comes judicial innocence of all sins, hence baptism gives us the answer of a “good suneidesis” rather a defiled one.
None of this implies that baptism is of ultimate benefit without wholehearted trust in God, persevering to the end. Peter says that “he that does not have these things is blind, and cannot see far off, and has forgotten the purging of his old sins.” The reality of the cleansing is in no doubt. But the suneidesis of a man who does not live a life of faithfulness to God is befouled. Peter adds, “Wherefore rather, brethren, give diligence to make your calling and election sure: for if ye do these things, ye shall never fall: for so an entrance shall be ministered unto you abundantly into the everlasting kingdom of our Lord and Savior Jesus Christ.” And if you don’t live that way, then you won’t enter, and you will fall.
So baptism really works, and it really cleanses your suneidesis. But it isn’t enough; you must walk worthy of that baptism, and live a life of faith. It is not a “get out of hell free” card.