I quote Dr. Hunt:
“The Old Testament places little emphasis on our becoming like God while the New Testament reiterates numerous injunctions to imitate God or to be like Christ. In its earliest pages, the Bible tells us that God created us in His image (Gen. 1:26; 5:1) Yet after Adam’s fall, the Old Testament has very little reference to our likeness to God and no admonitions to become like Him. The Old Testament emphasis is on the difference between God and man. ‘For My thoughts are not your thoughts, Neither are your ways My ways,’ declares the Lord. . . . The New Testament makes a radical shift in its emphasis. Here God in Christ is made like us: ‘Since then the children share in flesh and blood, He Himself likewise also partook of the same . . . . Therefore, He had to be made like His brethren in all things, that He might become a merciful and faithful high priest in things pertaining to God.’ (Heb. 2:14, 17). After redemption was accomplished, the New Testament picks up the theme from the opening chapters of the Bible, and once more we are to be like God. Paul said, ‘Put on the new self, created to be like God in true righteousness and holiness’ (Eph. 4:24, emphasis added).”
Our righteousness and holiness can come by the Counsel and Help of the Holy Spirit whom the resurrected Jesus sent as He promised to indwell believers in repentence, an indwelling that was lost at the Fall but restored by the love and grace of God through the sin sacrifice of Jesus Christ.