Because it is contained in Scripture, "Behold, I lay in Zion a chief cornerstone, chosen, and precious: He who believes in him will not be disappointed."
For they stumble at the word, being disobedient ...  There is much to commend the viewpoint of Macknight on this place, who wrote, "Peter does not mean that they stumbled at the preached word, but against Christ himself, one of whose titles is the Word (John 1:1)."[28]