My hunch is that few of us have had someone say, "Repent!" and received that as a positive thing. It sounds like scolding and none of us enjoy being scolded. But when Jesus announces the nearness of the Kingdom of God in Mark 1:15, the word repent is tied to the word gospel, or good news. "The time is fulfilled, the Kingdom of God is near; repent and believe the gospel."
I typically hear the word repent a little like the old song, "Santa Claus is Coming to Town." "You better watch out, you better not cry, you better not pout, I'm telling you why..." We receive it as a warning related to bad behavior. And when John the Baptist calls for repentance, its often attached to his dire warnings for the religious leaders who come to observe what is going on in the desert.
But I would point out precisely here that there were many who gladly received John's baptism of repentence. For them repentence was good news, and I think not because they felt particularly guilty about this or that sin. Rather, the appearance of an Elijah-type figure in the wilderness preaching baptism and forgiveness of sins signaled that the Kingdom of God might be finally coming. And that when the Kingdom of God comes, there might be a reversal of fortunes. The winners might be declared losers and the losers winners.
Jesus' announcement that the time is fulfilled and the Kingdom is near would certainly match this expectation. This announcement holds out the possibility that life might now be lived under different management. That regime change might be afoot. Those who benefit from the current power arrangements won't be happy, but those willing to turn their lives in the direction of the coming Kingdom of God will find themselves suddenly on the right side of history.
The Kingdom of God is not simply an improvement of conditions on the ground. The Kingdom of God is an alternative to those conditions. To belong to a new regime that exists as an alternative to all other power arrangements requires an entirely new set of commitments. To belong to the new age coming in the fullness of time necessitates more than change--it necessitates a turning, a reversal. One simply cannot stay the same and welcome the Kingdom of God.
So, repentance is the opportunity to align our lives with the interests of the coming reign of God. And to the extent that we believe that the Kingdom of God is peace and joy in the Holy Spirit, then the call to repentance will be received as good news. Repent and believe the good news.