Being a citizen of the world of Jesus to come is secured here on earth in His world by becoming an obedient citizen under His Shepherdess before we die. And we might even die before we die to secure it. Matthew 7:21

Revelation 3:21 ASV
He that overcometh, I will give to him to sit down with me in my throne, as I also overcame, and sat down with my Father in his throne.

Revelation 12:11 ASV
And they overcame him because of the blood of the Lamb, and because of the word of their testimony [witness] and they loved not their life even unto death.

What we must do HERE ON EARTH to become a citizen of the world of Jesus to come is not a mistery. Jesus told us how in the parable of the rich man and Lazarus. in Matthew 5:17-18 also.

Luke 16:27-31 ASV
(27) And he said, I pray thee therefore, father, that thou wouldest send him to my father's house;
(28) for I have five brethren; that he may testify unto them, lest they also come into this place of torment.
(29) But Abraham saith, They have Moses and the prophets; let them hear them.
(30) And he said, Nay, father Abraham: but if one go to them from the dead, they will repent.
(31) And he said unto him, If they hear not Moses and the prophets, neither will they be persuaded, if one rise from the dead.