"[Abraham] received the sign of circumcision as a seal of the righteousness that he had by faith while he was still uncircumcised. The purpose was to make him the father of all who believe without being circumcised, so that righteousness would be counted to them as well."
As I have demonstrated on this website, I am a paedobaptist. I know someone is asking, "Is that anything like a Southern Baptist?" But no, it's not. Rather, a paedobaptist (from the Greek words for "child" and "baptizer") is a person who believes in the baptism of the minor children of believers. This is in contrast to a credobaptist (from the Latin word for "belief" and "baptism," so "believer's baptism"). Paedobaptists include Catholics, Eastern Orthodox, Lutherans, Methodists, and Presbyterians, though for various different, even opposed, reasons. Credobaptists include Baptists (obviously!), most Pentecostals, Mormons, and Jehovah's Witnesses, again for various reasons.
I am, to be more specific, a Reformed Paedobaptist, so I do not necessarily endorse the explanations of others, especially Catholics and Eastern Orthodox. The resemblance between our rite and theirs is strictly coincidental.
The passage above refers back to the events of Genesis 17. I bring the specific verse above into the conversation because it explicitly states that circumcision is a seal, i. e., a sacramental sign, of righteousness by faith. Yet, Abraham was explicitly commanded to circumcise the infant and juvenile male members of his household (Gen. 17:12-13).
This aims directly at credobaptist objections to the baptism of infants. As water baptism is the sign and seal of righteousness by faith (I Peter 3:18-21), they say, it cannot be applied to infants, since they are incapable of believing.
That argument runs smack into the argument of Paul in this verse. Circumcision, he says, is this same sort of seal, yet it is to be applied to the infants of believers, who, as the Baptists insist, are themselves still incapable of belief (we will set aside the case of John the Baptist for this discussion, Luke 1:41). Therefore, there are no biblical grounds for withholding baptism from those same infants, under the New Covenant. Let me re-emphasize: if circumcision, as a seal of faith, was not to be withheld from the infants of believers, then neither is baptism to be withheld from them as such.
While he doesn't make the point in this passage, Paul's theology here is the same as that which he explains in I Corinthians 7:14: "the unbelieving husband is made holy because of his wife, and the
unbelieving wife is made holy because of her husband. Otherwise your
children would be unclean, but as it is, they are holy." The children of one or both believing parents are holy, not individually, because of the righteousness of faith, but rather federally, under the umbrella - so to speak - of their parent's or parents' faith. Thus, they were to be circumcised under the Old Covenant, and are to baptized under the New Covenant.
I think that this is a very clear refutation of the views of my credobaptist brethren. At the very least, they should have the charity to stop accusing Presbyterians of baptizing our children merely as a holdover tradition from Roman Catholicism.