When your son asks you in time to come, ‘What is the meaning of the testimonies and the statutes and the rules that the Lord our God has commanded you?’ then you shall say to your son, ‘We were Pharaoh’s slaves in Egypt. And the Lord brought us out of Egypt with a mighty hand. And the Lord showed signs and wonders, great and grievous, against Egypt and against Pharaoh and all his household, before our eyes. And he brought us out from there, that he might bring us in and give us the land that he swore to give to our fathers. And the Lord commanded us to do all these statutes, to fear the Lord our God, for our good always, that he might preserve us alive, as we are this day. And it will be righteousness for us, if we are careful to do all this commandment before the Lord our God, as he has commanded us.’

via Deuteronomy 6:20-25 – ESVBible.org.

So, when someone sins, were they therefore devoid of the “righteousness” that is promised “if we are careful to do all this commandment before the LORD our God as he has commanded us”?

Of course not. The testimonies, statutes, and rules contained promises of forgiveness on the basis of the understanding that God’s people are sinners who will always need forgiveness. The Law provides for all the forgiveness God’s people will need. It does not expect nor demand sinless moral perfection as a condition for possessing the righteousness promised in Deuteronomy 6.25. What it does demand is that Israelites not abandon the true god for a pagan pretend god.

And the LORD spoke to Moses, saying, “Speak to the people of Israel and say to them, I am the LORD your God. You shall not do as they do in the land of Egypt, where you lived, and you shall not do as they do in the land of Canaan, to which I am bringing you. You shall not walk in their statutes. You shall follow my rules and keep my statutes and walk in them. I am the LORD your God. You shall therefore keep my statutes and my rules; if a person does them, he shall live by them: I am the LORD (Leviticus 18.5)

Don’t entrust yourself to the gods of Egypt nor to the gods of Canaan, but rather trust the Lord.