Jamieson, Fausset and Brown on 1 Peter 1:15

15. Literally, "But (rather) after the pattern of Him who hath called you (whose characteristic is that He is) holy, be (Greek, 'become') ye yourselves also holy." God is our grand model. God's calling is a frequently urged motive in Peter's Epistles. Every one that begets, begets an offspring resembling himself [Epiphanius]. "Let the acts of the offspring indicate similarity to the Father" [Augustine].

conversation--deportment, course of life: one's way of going about, as distinguished from one's internal nature, to which it must outwardly correspond. Christians are already holy unto God by consecration; they must be so also in their outward walk and behavior in all respects. The outward must correspond to the inward man.