He likely means the levitial law which speaks of sinning in ignorance (versus wilfully) and there always seemed to be forgiveness for a sin through ignorance.
- [2] Speak unto the children of Israel, saying, If a soul shall sin through ignorance against any of the commandments of the LORD concerning things which ought not to be done, and shall do against any of them:
- [13] And if the whole congregation of Israel sin through ignorance, and the thing be hid from the eyes of the assembly, and they have done somewhat against any of the commandments of the LORD concerning things which should not be done, and are guilty;
- [22] When a ruler hath sinned, and done somewhat through ignorance against any of the commandments of the LORD his God concerning things which should not be done, and is guilty;
- [27] And if any one of the common people sin through ignorance, while he doeth somewhat against any of the commandments of the LORD concerning things which ought not to be done, and be guilty;
- [15] If a soul commit a trespass, and sin through ignorance, in the holy things of the LORD; then he shall bring for his trespass unto the LORD a ram without blemish out of the flocks, with thy estimation by shekels of silver, after the shekel of the sanctuary, for a trespass offering:
- [24] Then it shall be, if ought be committed by ignorance without the knowledge of the congregation, that all the congregation shall offer one young bullock for a burnt offering, for a sweet savour unto the LORD, with his meat offering, and his drink offering, according to the manner, and one kid of the goats for a sin offering.
- [25] And the priest shall make an atonement for all the congregation of the children of Israel, and it shall be forgiven them; for it is ignorance: and they shall bring their offering, a sacrifice made by fire unto the LORD, and their sin offering before the LORD, for their ignorance:
- [27] And if any soul sin through ignorance, then he shall bring a she goat of the first year for a sin offering.
- [28] And the priest shall make an atonement for the soul that sinneth ignorantly, when he sinneth by ignorance before the LORD, to make an atonement for him; and it shall be forgiven him.
- [29] Ye shall have one law for him that sinneth through ignorance, both for him that is born among the children of Israel, and for the stranger that sojourneth among them.
Same with the Israelites and their rulers, Peter acknowledges it was through ignorance
Acts 3:17
And now, brethren, I wot that through ignorance ye did it, as did also your rulers.
The Gentiles and their ignorance (God winked at) but now commands them to repent
Acts 17:30
And the times of this ignorance God winked at;
but now commandeth all men every where to repent
Earlier with the Gentiles worship in ignorance
Acts 17:23 For as I passed by, and beheld your devotions, I found an altar with this inscription, TO THE UNKNOWN GOD.
Whom therefore ye ignorantly worship, him declare I unto you
Fashioning ourselves in a former lusts in our ignorance is also show
1 Peter 1:14
As obedient children,
not fashioning yourselves according to the former lusts in your ignorance
Paul even says, he obtained mercy because he did what he did ignorantly in unbelief
1 Ti 1:13
Who was before a blasphemer, and a persecutor, and injurious: but I obtained mercy, because I did it ignorantly in unbelief
Then there is wilfully sinning, not sure where to find that in the OT, just here
Heb 10:6
For if we sin wilfully after that we have received the knowledge of the truth, there remaineth no more sacrifice for sins
Edit:typo