To change radically in inner character, condition, or nature. In <Romans 12:2> the apostle Paul exhorted Christians, "Do not be conformed to this world, but be transformed by the renewing of your mind." Followers of Christ should not be conformed, either inwardly or in appearance, to the values, ideals, and behavior of a fallen world. Believers should continually renew their minds through prayer and the study of God's Word, by the power of the Holy Spirit, and so be transformed and made like Christ <2 Cor. 3:18>. When He returns, Christ will "transform our lowly body that it may be conformed to His glorious body" <Phil. 3:21>.
In <2 Corinthians 11:13-15> Paul warned his readers to beware of "false apostles, deceitful workers, transforming themselves into apostles of Christ" <v. 13>. One should not be surprised, said Paul, at such false apostles-- people who are counterfeit and phony but who wear masks to deceive others-- for "Satan himself transforms himself into an angel of light" <v. 14>. Satan's workers, in imitation of their ruler, also disguise themselves as agents of good.
(from Nelson's Illustrated Bible Dictionary)
(Copyright (C) 1986, Thomas Nelson Publishers)