you have to have heaven in you now to be there when you die 2

Think about it: people who literally have the understanding and vision of the afterlife of heaven and glorification in them as they exist in their everyday lives are the people who you don't have difficulty thinking about being in heaven when they physically die.

On the other hand: people who never visualize such things as heaven and glorification and who don't live the life of engaging Scripture and Wisdom and prayer and fasting and meditation, yet who may very well be professional theologians or church leaders or very active, self-identified Christians --- these people you do have difficulty thinking of them being in heaven when they physically die. You tend to actually really think that they will recur in the mechanical, sleeping state they left in.

It's a powerful practice, though, to visualize what the Bible promises. This is something you can use systematic theology for because systematic theology really isolates and describes each thing the Bible presents and makes it so that you can focus on each one and visualize having it, or being in it, or experiencing it. The fact is: you can't be something or enter into something that you can't visualize (which by "can't visualize" is meant: that you are asleep to and have no consciousness of or understanding of and hence no real valuation for).