Are believers changed into Christ's image outwardly or inwardly, and who does the changing?
Believers are changed inwardly, not outwardly. God sees the inward transformation, and they have already been transfigured into the same image from glory to glory. The Spirit of the Lord does the changing, not the Law. Believers behold Christ as in a mirror, and the world sees His reflection.
Les explains that this change is not shown outwardly, but God sees it inwardly. Believers have already been transfigured into the same image from glory to glory, even by the Spirit of the Lord. He contrasts Israel, which was veiled from the truth of the Law and could not see it fading away, with believers who with open face behold as in a glass the glory of the Lord. As we look at Christ like in a mirror, the world sees His reflection. The Law could never do that, because Moses had to be veiled and Israel could never understand; believers are not under Law but under grace.
But we all, with open face beholding as in a glass the glory of the Lord, are changed into the same image from glory to glory, even as by the Spirit of the LORD.