If the new heavens and new earth are not coming to pass, if Jesus was a liar (or simply crazy) and there is no resurrection of the dead, if this world and this biological life is all that there is, then you had better live for yourself. You should get all the pleasures you can right now, because there isn't anything better coming down the road. There is no need for any morality, any service, because life is too short wasting it on anything that doesn't give you what you want for yourself.
But if the Last Day is coming, if Jesus is coming back just as He said, if He truly was raised from the dead, the firstfruits of them that fall asleep, then you are free to live for others. Not to earn your way into this eternal bliss; that would simply be slavery once again. That's the bondage of selfishness. No, truly free. This world's pleasures are fleeting, they have nothing to compare with what is coming, and so there is nothing worth pursuing in this life for one's own gain. You can be turned completely outside of yourself to the needs of others.
If you live for others, you will taste eternity, for in the new heavens and the new earth there is no more selfishness, no more pride. If you live for others you will suffer; you will suffer the scorn of a world that seeks its own way, you will suffer from carrying the burdens of others. But suffering comes before glory, and the glory that is to come is incomparable with the suffering that preceded it.
The eyes fixed on the horizon, looking for the returning Christ, see the neighbor more clearly than those with their eyes fixed on the ground, curved inward on themselves.
Of course, we don't do this; we live for ourselves, for being curved in on ourselves is our natural condition. That is why Christ delivers forgiveness to us; repentance and forgiveness is the rythm of the Christian's baptismal life. He turns us away from ourselves to Him and His cross, His blood-bought forgiveness, and when we look to Him, then He shows us our neighbor in need. And we serve, stumbling, imperfectly, but forgiven and perfected by His death and His resurrection. We live in light of His resurrection and the sure and certain hope of our resurrection guaranteed by the empty grave. Come, Lord Jesus!