What does "repent" really mean?

When we hear the word “repent,” we each probably have an image or idea about what it means—what it looks like. But it is always better to find out what the Bible really has to say about it. I use the Amplified version along with the King James (I have a side-by-side parallel edition) so I can see what the key words really mean. I chose five verses to help us understand what God means by repentance.
Joel (2:12 AMP) talks about repentance this way: “Therefore also now, says the Lord, turn and keep on coming to Me with all your heart, with fasting, with weeping, and with mourning [until every hindrance is removed and the broken fellowship is restored].”
Matthew records what John the Baptist was telling the people in Judea during the initial days of Jesus’ ministry: “. . . Repent (think differently; change your mind, regretting your sins and changing your conduct), for the kingdom of heaven is at hand (Matthew 3:2 AMP).
The physician, Luke, writes about repentance in several places in the Book of Acts. He records Peter’s answer to those wanting to know what was happening on the day that the Holy Spirit was poured out on the Jesus-followers: “Repent (change your views and purpose to accept the will of God in your inner selves instead of rejecting it) and be baptized, every one of you, in the name of Jesus Christ for the forgiveness of and release from your sins; and you shall receive the gift of the Holy Spirit” (Acts 2:38 AMP). Peter continues a little later, “So repent (change your mind and purpose); turn around and return [to God], that your sins may be erased (blotted out, wiped clean), that times of refreshing (of recovering from the effects of heat, of reviving with fresh air) may come from the presence of the Lord (Acts 3:19 AMP).
Then Paul explains the difference between biblical repentance and just being sorry about getting caught doing wrong. “For godly grief and the pain God is permitted to direct, produce a repentance that leads and contributes to salvation and deliverance from evil, and it never brings regret; but worldly grief (the hopeless sorrow that is characteristic of the pagan world) is deadly [breeding and ending in death] (2 Corinthians 7:10 AMP).
If we have truly repented, our lives should reflect the change of thinking and doing. Selah (pause and calmly think of that!).