The law and the prophets were until John: since that time the kingdom of God is preached, and every man presseth into it. Luke 16:16
And he said unto them, I must preach the kingdom of God to other cities also: for therefore am I sent. Luke 4:43
And he sent them to preach the kingdom of God, and to heal the sick. Luke 9:2
And the people, when they knew it, followed him: and he received them, and spake unto them of the kingdom of God, and healed them that had need of healing. Luke 9:11
Jesus said unto him, Let the dead bury their dead: but go thou and preach the kingdom of God. Luke 9:60
And Jesus said unto him, No man, having put his hand to the plough, and looking back, is fit for the kingdom of God. Luke 9:62
But rather seek ye the kingdom of God; and all these things shall be added unto you. Luke 12:31
And when one of them that sat at meat with him heard these things, he said unto him, Blessed is he that shall eat bread in the kingdom of God. Luke 14:15
Neither shall they say, Lo here! or, lo there! for, behold, the kingdom of God is within you. Luke 17:21
What do you think they preached, preaching the Kingdom of God? Looks like thats what Jesus preached and told followers to preach. It doesn't seem if someone asked Jesus about sin in his or her life. His reply wouldn't be, oh its ok you are only human, you all are sinners. Maybe when they preached the Kingdom of God, they spoke of things that wouldn't be entering as well.