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."

 Jesus himself had said--and doubtless the saying was in Peter's mind: "Let your light so shine before men that they may see your good works and give glory to your Father who is in heaven" ( Matthew 5:16). This was a line of thought which the Jews knew well. In one of the books written between the Old and the New Testaments it says: "If ye work that which is good, my children, both men and angels shall bless you; and God shall be glorified among the Gentiles through you, and the devil shall flee from you" (The Testament of Naphtali 8: 4). 