Joshua 5:1–10 has something to say regarding the place of sacraments in God’s plans and purposes for his people.
Israel's refusal to circumcise was an act of unbelief.
In Joshua 5:2–9, the people of Israel must be circumcised. The unbelief of the first generation meant that the second generation did not bear the sign and seal of the covenant of grace. They did not bear the mark of belonging to God. The refusal of the first generation to give the covenant sign to their covenant children was an act of unbelief. The fact that this was sinful unbelief is emphasized by the mention of flint knives in verse 3. The only other place in the Old Testament where flint knives are associated with cutting, also concerns circumcision. In Exodus 4:24 the Lord sought to kill Moses, and his anger was stopped only when Zipporah took a flint and cut off their son’s foreskin.
Refusal to baptize children is likewise an act of unbelief.
According to Colossians 2:11–12, baptism has replaced circumcision as the sign of belonging to the covenant of grace. This is what Reformed churches confess. As a result, since it was a sinful act of unbelief to refuse the covenant sign to covenant children in the Old Testament, the same holds true today. The neglect of baptism is a sinful act of unbelief.
1 As soon as all the kings of the Amorites who were beyond the Jordan to the west, and all the kings of the Canaanites who were by the sea, heard that the LORD had dried up the waters of the Jordan for the people of Israel until they had crossed over, their hearts melted and there was no longer any spirit in them because of the people of Israel.