If my end was ultimately exactly the same as the end of someone who didn't serve God, what motivation would I have to live in the self-sacrificing, often difficult way that God commands? Imagine the most selfish, wicked, God-defying wretch you can think of - a Colombian drug lord, or Russian criminal oligarch, or Hitler, or Stalin - serving every perverse impulse that grips them, killing millions of other people, etc. who, after a life of evil selfishness just...stops, their body dying and their consciousness ceasing forever. They encounter no Final Judgment, no accounting to God for their evil, no divine justice rendered upon their sin; they just wink out of existence permanently. Have they not, essentially, gotten away with a life of great wickedness? And what of the Mother Theresa type who toils away in a life of deep self-sacrifice, suffering pain and deprivation to help the downtrodden and persecuted, who contracts a deadly disease from one of the people she's helped and dies, her consciousness evaporating into nothing forever? Her end is just the same as the one who has lived exactly the opposite sort of life from hers. If there is nothing after this life, if the end of the wicked and the righteous is the same, "eat, drink and be merry, for tomorrow we die!"
But, thank God, this isn't the case. "It is appointed unto man once to die and after this, the Judgment." (Hebrews 9:27) We all go on either to eternal "joy inexpressible and full of glory" in God's heavenly kingdom, or to eternal, conscious torment in hell, separated from God (and all others), in "the blackness of darkness forever." (Jude 1:13)