Therefore, if anyone is in Christ, he is a new creation; old things have passed away; behold, all things have become new. 2 Corinthians 5:17 (NKJV)
The day you believed in your heart and confessed the Lordship of Jesus Christ with your mouth, you were saved. Though nothing changed outwardly, your spirit man was renewed. If a man continues living in Christ (abides), the change within begins to reflect without. Those who knew Christ in the flesh knew Him no longer when He rose from the dead because renewal happened when the flesh died. Transformation happens when we die to the flesh daily and allow the life of Christ to take the center stage in our lives.
Holy Express
Acts 1:3 describes how Jesus presented Himself to His disciples after being raised from the dead and gave many convincing proofs that He was alive. Jesus had to prove His resurrection because the glory of God upon Him had changed Him. This is the true meaning of becoming a new creation or being Christ like. The secret to transformation is found in the next verses, Acts 1:4-5. The Holy Spirit bears witness with our spirits that we are children of God and joint-heirs with Christ, thus helping us to think, talk and walk like Him.