I am going to have to read the book because I still don't understand what you're saying the difference is. I don't see why the covenant of grace can't begin in the garden and still have believers baptism.
A clue is uncovered by contemplating why it was punishable with death if the father failed or refused to apply the sign of the covenant to his male children, namely, circumcision. Consider the example of Moses, where God sought to kill him for failing to circumcise his son (Exo 4:24-26). The note in the New English Translation explains it thus:
The point is that this son of Abraham [i.e., Moses] had not complied with the sign of the Abrahamic covenant. No one, according to Exodus 12:40-51, would take part in the Passover-exodus who had not complied. So, how could the one who was going to lead God’s people not comply? The bold anthropomorphisms and the location at the border invite comparisons with Genesis 32, the angel wrestling with Jacob. In both cases there is a brush with death that could not be forgotten.
In the
Brazos Theological Commentary on the Bible (2016) for the book of Exodus, they explain:
[This passage] here is emphasizing in a very primitive and visceral way the rectitude necessary for a right relationship with God. Obedience to God must be conducted on God's terms and not conventional human terms. Induction into the covenant of God occurs through circumcision. Moses is not excepted from the patriarchal custom, or from the law of God, but is subject to God like everyone else, and even more so.
The text stands as a warning against the presumption of religious leaders who might come to think they are excused from the observance of the commandments of God. God is far more terrifying than Pharaoh. He is the author of life and death; God is good, but he is also sovereignly just. Here we see a foreshadowing of the coming of the Lord to slay the firstborn, as a punishment of the Egyptians (Exo 11:4). The Israelites will be spared because they place the blood of the Passover lamb upon their doorposts (12:7). Typologically, circumcision prefigures baptism, while the Passover lamb signifies the Eucharist. ... It is seriously presumptuous for a person to presuppose that he or she can knowingly forgo the means of salvation divinely instituted by Jesus Christ and yet still obtain the grace of salvation. On the contrary, such behavior is liable to judgment since it constitutes a very serious act of disobedience to supernatural faith in Christ.
The importance of circumcision in the Old Testament was rooted in its significance as a sign of the covenant between God and Abraham's descendants. It was considered so crucial that even during times of travel or potential danger, the ritual was expected to be performed. It applied not only to one's own children but also to servants and others in the household. The covenant was meant to be universally applied to all males under the authority of the head of the household.
This ought to illustrate why it is not safe to refuse applying the sign of the covenant to our children—or why we can't have just credobaptism alone. God sets the terms of the covenant, and we bow our heads and say, "As you will, Father."
Children are sanctified by their parents in the Bible, isn't it?
Baptism does not necessarily produce sanctification—not even for credobaptists. However, like circumcision, it is a sign of the covenant of grace. Like circumcision, baptizing children inaugurates them into the visible covenant family of God, setting them apart in the world (1 Cor 7:14) and placing them under the means of grace. It is the means of grace—the preaching and teaching of God's word, baptism, and the eucharist—that God uses to regenerate and sanctify his children.
This understanding is based on passages like 1 Corinthians 7:14, where Paul states that the children of a believing parent are "holy" (set apart), and Genesis 17, where God commanded circumcision as a covenant sign for infants in Abraham’s household. Since baptism is seen as the New Testament fulfillment of circumcision (cf. Col 2:11–12), children of believers are baptized to signify their inclusion in the covenant community.
However—and credobaptists affirm this, too—while baptism places them in a privileged position, they still need to personally embrace Christ through faith in order to receive salvation. But, again, being a member of the covenant community places the child under the means of grace through which God does exactly that.
And yes, of course my husband listed reasons.
I suspected as much, as my response indicated. Sounds like a great man. You are blessed by God.
I will remind him not to conflate Presbyterian with Reformed and I'll avoid quoting him. My apologies.
Or, alternatively, ask him if there is any difference between Reformed and Presbyterian. Again, I suspect he already understands.
And there is no need to stop telling us, "My husband said ...," and no need to apologize for having done so. I am certain that, here, you are in the company of people who don't judge him based on your quotes. You are simply citing your sources.