Mark 10:21 is informative about what to think about heaven, but it must be read in context and I’m asking you to read the whole text carefully — there’s a lot here and this passage directly addresses our concern. Is heaven a place to which we go when we die? What is heaven? :

17 As Jesus started on his way, a man ran up to him and fell on his knees before him. ?Good teacher,? he asked, ?what must I do to inherit eternal life?? 18 ?Why do you call me good??

Jesus answered. ?No one is good?except God alone. 19 You know the commandments: ?Do not murder, do not commit adultery, do not steal, do not give false testimony, do not defraud, honor your father and mother.? ?
20 ?Teacher,? he declared, ?all these I have kept since I was a boy.?
21 Jesus looked at him and loved him. ?One thing you lack,? he said. ?Go, sell everything you have and give to the poor, and you will have treasure in heaven. Then come, follow me.?
22 At this the man’s face fell. He went away sad, because he had great wealth.
23 Jesus looked around and said to his disciples, ?How hard it is for the rich to enter the kingdom of God!? 24 The disciples were amazed at his words. But Jesus said again, ?Children, how hard it is to enter the kingdom of God! 25 It is easier for a camel to go through the eye of a needle than for a rich man to enter the kingdom of God.? 26 The disciples were even more amazed, and said to each other, ?Who then can be saved?? 27 Jesus looked at them and said, ?With man this is impossible, but not with God; all things are possible with God.? 28 Peter said to him, ?We have left everything to follow you!? 29 ?I tell you the truth,? Jesus replied, ?no one who has left home or brothers or sisters or mother or father or children or fields for me and the gospel 30 will fail to receive a hundred times as much in this present age (homes, brothers, sisters, mothers, children and fields?and with them, persecutions) and in the age to come, eternal life. 31 But many who are first will be last, and the last first.?

First, we need to connect these terms: eternal life, kingdom of God, heaven, and saved.
Second, eternal life is clearly connected with the age to come in v. 30.
Third, eternal life/age to come are distinguished from “this present age” in vs. 30.
It won’t do to say “eternal life” means abundant life in the now; it may be abundant life in the now but that life is a life connected to the age to come.
Fourth, is heaven the age to come? Is heaven the kingdom of God? is heaven this present age?
In my judgment, the evidence of this text focuses “heaven” on eternal life (Jesus’ answer to the man’s question) and the age to come (v. 30).
Fifth, Jesus emphasize both now and the future, neither at the expense of the other.
Finally, if heaven is connected to eternal life and the age to come, then it is a place into which one enters in the future. Is it after death? Perhaps. Is it on earth? Perhaps.
We must be willing to entertain the option that “heaven” in Jesus’ language might be what later NT authors call “the new heaven and the new earth.” We must also be willing to entertain the option that it could refer to the earthly kingdom of God.