For those who believe in Jesus, eternity includes life everlasting in God's presence, free from pain and sorrow, with a future resurrection and life on a new earth.
Eternity is not a one day or few years thing. It refers to everlasting existence. For as long as the Lord lives. All mankind though understand that God lives forever and ever. This means that eternal existence can not be measured in earthly years or times, not millions, not trillions and not even zillions of years can be used to equate what eternity means.
This is the most important thing to understand as it informs how you live your life. Another crucial thing to note is that there are two destinations or simply places where mankind ever created by God will spend their eternity. Either Heaven with God forever or in hell in constant and eternal damnation and also to understand that the place where mankind will spent their eternity is being determined by what they do here on earth. That death is not the end of all things but simply a door to another realm of reality. A realm of eternal existence.
A majority of Christians have made the world their permanent home and have totally forgotten the fact that we are mere mortals and sojourners on this earth that is passing away. They have taken a salvation of convenience and have become reluctant to prepare for that day when they will be recalled.
Ecclesiastes 3
10I have seen the burden God has laid on the human race. 11He has made everything beautiful in its time. He has also set eternity in the human heart; yet a no one can fathom what God has done from beginning to end.Â
The Lord at His creation of mankind, embedded eternity in them. in the beginning however His intentions were to fellowship with mankind forever. At the fall when disobedience set in two either of two destinations became the fate of mankind. Eternity in heaven or in hell.
The Lord however because of His love rolled out the salvation plan for Humanity by giving out Jesus that whosoever believes in Jesus will have everlasting life with God. The veice versa is true for those who will not take Jesus and the Salvation He brought. They will end up in eternal damnation where there will be weeping and gnashing of teeth.