Charles Ellicott Commentary 1 Peter 1:16

"because it is written, Ye shall be holy; for I am holy." — 1 Peter 1:16 (ASV)

Be you holy; for I am holy.—The better reading here is, You shall be holy; it is still, however, a command, not a promise—except that all God’s commands are promises. The command comes some five or six times in the Book of Leviticus, addressed not only to the Levites, but to all the people. It would, therefore, apply twice over to the recipients of this letter by virtue of their twofold consecration, in the old and in the new Israel.