1 Peter 1:5

kept--Greek, "who are being guarded." He answers the objection, Of what use is it that salvation is "reserved" for us in heaven, as in a calm secure haven, when we are tossed in the world as on a troubled sea in the midst of a thousand wrecks? [CALVIN]. As the inheritance is "kept" (Pe1 1:4) safely for the far distant "heirs," so must they be "guarded" in their persons so as to be sure of reaching it. Neither shall it be wanting to them, nor they to it. "We are guarded in the world as our inheritance is kept in heaven." This defines the "you" of Pe1 1:4. The inheritance, remember, belongs only to those who "endure unto the end," being "guarded" by, or IN "the power of God, through faith." Contrast Luk 8:13. God Himself is our sole guarding power. "It is His power which saves us from our enemies. It is His long-suffering which saves us from ourselves" [BENGEL]. Jde 1:1, "preserved in Christ Jesus"; Phi 1:6; Phi 4:7, "keep"; Greek, "guard," as here. This guarding is effected, on the part of God, by His "power," the efficient cause; on the part of man, "through faith," the effective means. by--Greek, "in." The believer lives spiritually in God, and in virtue of His power, and God lives in him.

— Jamieson-Fausset-Brown Commentary (public domain)