This is a very important question.  Assuming eternity lasts a very long time, this is a subject to ponder.  Some religions don't teach about heaven or a hereafter.  They just figure we live, we die, then nothingness.  We addressed this in the previous question and answer.
 
Among the overwhelming majority of preachers, priests, pastors, etc. who consider themselves to be Christian, they teach that after we die, we can expect to spend eternity in heaven or hell.

A frequent question these preachers, priests, and pastors have to answer goes something like this:
"How could an all loving God let anyone go to hell?"

The truth of the matter is that God is very loving. But God doesn't love sin.  God also has other qualities.  God is Holy and God is Just.

God's desire (Love) is that all should be saved.  He sent His Son into the world to pay for our sins (satisfying His need for Justice), and to cover us with the blood Jesus shed (satisfying His need for Holiness).




Bible References
Pondering
Heaven ?
Is everyone going to heaven?
And the LORD spoke to Moses, saying, "Speak to all the congregation of the children of Israel, and say to them: 'You shall be holy, for I the LORD your God am holy.     (Leviticus 19:1-2 NKJV)

God is a just judge, And God is angry with the wicked every day.
(Psalms 7:11 NKJV)

For God so loved the world that He gave His only begotten Son, that whoever believes in Him should not perish but have everlasting life.  For God did not send His Son into the world to condemn the world, but that the world through Him might be saved.
(John 3:16-17 NKJV)

For He made Him who knew no sin to be sin for us, that we might become the righteousness of God in Him.
(2 Corinthians 5:21 NKJV)