I don't believe in religion ... religion is just a disciplined way to serve God and we don't all have the same God, but I do believe in a personal relationship with Jesus, the son of God. Who promises a judgement day ... a judgement day for our sins.
Religion also has different forms of rewards and promises such as the Muslims for being a martyr and receiving 72 virgins or a Buddha lover or a Hindu lover and believing in reincarnation.
So if you believe in a reward for your behaviour you will more than likely behave.
What's to keep a non believer in going berserk and wiping out his or her entire family? What about the senior Army general's in charge of nuclear weapons that don't believe in a punishment phase and of course think that this life is all there is?
What's to keep them from wiping an entire civilization?
That's why I believe there is an invisible hand on every believer and non believer since time began or we are all doomed to the will of a crazy general or admiral or submarine captain out there in the deep blue sea.
King Solomon said it best: Ecclesiastes 3
To every thing there is a season,
and a time to every purpose under the heaven:
2 a time to be born, and a time to die;
a time to plant, and a time to pluck up that which is planted;
3 a time to kill, and a time to heal;
a time to break down, and a time to build up;
4 a time to weep, and a time to laugh;
a time to mourn, and a time to dance;
5 a time to cast away stones,
and a time to gather stones together;
a time to embrace, and a time to refrain from embracing;
6 a time to get, and a time to lose;
a time to keep, and a time to cast away;
7 a time to rend, and a time to sew;
a time to keep silence, and a time to speak;
8 a time to love, and a time to hate;
a time of war, and a time of peace.
and then again in verse 3:13
And also that every man should eat and drink, and enjoy the good of all his labour, it is the gift of God.