Abraham believed God & God made a covenant with him. (Gen. 15:6 & 18) That covenant was based on the fact that Abe believed God. Now he’s God’s friend, as well as his covenant partner.
But in Genesis 12, Abe is afraid & lies about Sara. He was afraid the king would kill him to get his hands on his hot wife, so he says, “She’s my sister, not my wife!”
Abraham is giving in to a spirit of fear, and he’s a liar. Those are bad. But God backs him up, IN THE LIE! He defends Abraham (and his marriage) from the ignorant, horny kings.
Wait, what? God defends the liar? And defends the lie? Why would he do that?
It was hundreds of years later that Moses comes down the mountain with The Law, which includes “Don’t sleep with another man’s wife,” and “Don’t tell lies” and such. Now, with coming of The Law, adultery and lying (and several other things) become a sin.
The Law is a part of Moses’ covenant with God. It’s not part of Abraham’s covenant with God, or Noah’s.
In Abraham’s day, there was no rule that said “Don’t sleep with his wife,” and no rule that said, “Do not bear false testimony.” These rules didn’t show up until late in Moses’ life. They weren’t forbidden in Abraham’s day.
Were they still stupid things to do? Of course. And Abraham paid the price for that. But they weren’t “wrong” in Abe’s day and age.
So it’s not appropriate (or even meaningful) to judge Abraham or Noah by a covenant that didn’t exist in their day. In the same way, it’s not appropriate to judge a Peruvian farmer by Norway’s laws, or to judge a Mostho factory worker based on Peruvian law.
And The Law not actually part of our New Covenant either. Therefore, it’s completely inappropriate to judge New Covenant believers by Moses’ covenant. Or Noah’s covenant. Or any other covenant.
Are you a New Covenant believer? Then it’s completely inappropriate to judge yourself by Moses’ covenant either.