Acts 3:17

And now, brethren, I know that in ignorance ye did it, as did also your rulers. But the things which God foreshadowed by the mouth of all the prophets, that his Christ should suffer, be thus fulfilled.

In ignorance ye did it ... This extenuation of the guilt of Israel was mentioned by Peter for the sake of a more persuasive appeal to his hearers; and, of course, what Peter said of their being ignorant is true. However, Peter was not specific about the area of their ignorance, which was limited, especially as regards the rulers. The leaders of Israel knew that Christ was the long-expected Messiah, a holy and righteous man, and that he was the heir of the theocracy, and the rightful claimant of the throne of David - all this they most certainly knew; because, as Jesus said of them that they said among themselves, "This is the heir; come let us kill him, and the inheritance shall be ours" (Mark 12:7). The exact point of their ignorance regarded the fact of Jesus' being God come in the flesh, the very person who would judge them in the last day; THAT they did not know. The infinite patience and forbearance of God appear in Peter's making every possible allowance in softening the guilt of Israel's rejection of Christ.

That his Christ should suffer, be thus fulfilled ... Moreover, Peter stated here that their ignorant rejection had also fulfilled the prophecies of Jesus' sufferings. Having thus tempered, to the extent it was possible, the guilt of those who rejected and crucified the Christ, Peter at once appealed to them to obey the gospel, announcing the very same terms of salvation which he had previously spoken on Pentecost.