Macbeth is far more worried about the consequences of his actions in his present life on earth than any threat of eternal punishment, an attitude that would have marked him as a very evil man for the audience of Shakespeare's day. In his speech at the beginning of Act I, Scene 7, he states clearly that if he could be assured that the killing of Duncan could be done without risk to himself in the here and now,

But here, upon this bank and shoal of time,
We'd jump the life to come. But in these cases
We still have judgement here....

The last line of the quote indicates clearly that it is "judgment here," that is in the mortal world, that gives Macbeth pause. He develops four reasons why this "judgment" might be difficult to evade. The first is that as a person who wishes to be king, he sets a bad example by murdering a king:

This even-handed justice
Commends the ingredients of our poison'd chalice
To our own lips.

In other words, someone else will follow Macbeth's lead and murder Macbeth in his turn. The second and third reasons are that he would outrage moral standards by murdering Duncan, who is at the same time his relative, his ruler, and his guest. The fourth and last is that Duncan, for all his faults, has been a much-loved ruler:

Besides, this Duncan
Hath borne his faculties so meek, hath been
So clear in his great office, that his virtues
Will plead like angels trumpet-tongued against
The deep damnation of his taking-off

Macbeth has no motive other than his own ambition, and so he fears general condemnation if he removes Duncan.

Thus, while Macbeth dismisses divine punishment after death out of hand, he has detailed and well-grounded reasons to fear the reaction of his contemporaries in the mortal world.