21 Not every one that saith unto me, Lord, Lord, shall enter into the kingdom of heaven; but he that doeth the will of my Father which is in heaven.
Not all will be allowed back into the kingdom of heaven but they who do the will of our Father in Heaven. It is the will of our Father in Heaven that we repent and forsake our sins and keep his commandments.
Luke 13:23-24
23 Then said one unto him, Lord, are there few that be saved? And he said unto them,
24 Strive to enter in at the strait gate: for many, I say unto you, will seek to enter in, and shall not be able.
25 When once the master of the house is risen up, and hath shut to the door, and ye begin to stand without, and to knock at the door, saying, Lord, Lord, open unto us; and he shall answer and say unto you, I know you not whence ye are:
26 Then shall ye begin to say, We have eaten and drunk in thy presence, and thou hast taught in our streets.
27 But he shall say, I tell you, I know you not whence ye are; depart from me, all ye workers of iniquity.
28 There shall be weeping and gnashing of teeth, when ye shall see Abraham, and Isaac, and Jacob, and all the prophets, in the kingdom of God, and you yourselves thrust out.
Luke 13:1-5
1 There were present at that season some that told him of the Galilæans, whose blood Pilate had mingled with their sacrifices.
2 And Jesus answering said unto them, Suppose ye that these Galilæans were sinners above all the Galilæans, because they suffered such things?
3 I tell you, Nay: but, except ye repent, ye shall all likewise perish.
4 Or those eighteen, upon whom the tower in Siloam fell, and slew them, think ye that they were sinners above all men that dwelt in Jerusalem?
5 I tell you, Nay: but, except ye repent, ye shall all likewise perish.
Matthew 4:17
17 From that time Jesus began to preach, and to say, Repent: for the kingdom of heaven is at hand.