Repent -- among the very first words spoken by both John the Baptist and Jesus when they began their mission.

Matt. 3:1,2 John the Baptist, preaching in the wilderness of Judaea,
came saying, Repent ye: for the kingdom of heaven is at hand.

Matt. 4:17 Jesus began to preach, and to say, Repent: for the kingdom of heaven is at hand.
Mark 1:14-15 Jesus came into Galilee, preaching the gospel of the kingdom of God, And saying, The time is fulfilled, and the kingdom of God is at hand: repent ye, and believe the gospel.

Mark 6:7,12 And he called unto him the twelve, and began to send them forth by two and two; And they went out, and preached that men should repent.
Mark 13:2-6 Jesus answered them, ...except ye repent, ye shall all likewise perish. ..Do you think they were worse sinners than you... no, except ye repent, ye shall likewise perish.

Repent, is also what the apostles preached.

Acts 2:38 Then Peter said unto them, Repent, and be baptized every one of you in the name of Jesus Christ for the remission of sins, and ye shall receive the gift of the Holy Ghost.
Acts 3:19 Repent ye therefore, and be converted, that your sins may be blotted out, when the times of refreshing shall come from the presence of the Lord
Acts 17:30-31 And the times of this ignorance God winked at; but now
commands all men every where to repent: Because he has appointed a day, in which he will judge the world in righteousness

Why do we seldom here this anymore? Has it really been rejected?
One excuse we hear, is that it sounds too much like something we need to do, and isn't salvation all done for us?

What does it mean to repent? Is it really something we need to "do"?

Yet repentance is "big" in the Bible. It's an important ingredient in the battle against sin.

Then again we hear, "oh but it's a gift from God, it's not something we "do".
Yes, it is a gift
and scripture says in Romans 2:4 Do you despise the riches of his goodness and forbearance and longsuffering; not knowing that the goodness of God leads you to repentance?

So we do need to respond to His goodness and forbearance and not turn away from repentance. To turn away is actually "hardening our hearts" against Him! It's not that repentance is somehow secondary to the gospel or an addition to the gospel, it's at the very heart of the gospel. We can't even begin to understand the gospel if we don't understand our need for God's grace and our need to repent.

It sounds like a command: "repent ye", "men should repent", "now commands all men to repent"...