Our Lord's admonition to men to become perfect, even as the Father is perfect (Matt. 5:48) cannot rationally be construed otherwise than as implying the possibility of such achievment. Plainly, however, man cannot become perfect in mortality in the sense which God is perfect as a supremely glorified Being. It is possible, though, for man to be perfect in his squere and in a sense of analogous to that in which superior intelligences are perfect in their several spheres; yet the relative perfection of the lower is infintely inferior to that of the higher.
Elder James E. Talmage, Jesus The Christ, page 248, note 5