How God rewards unselfishness

The most direct route to personal happiness is through unselfish service to God and others. Why? Because of the gracious reward God bestows on the selfless.

This quote from Jonathan Edwards explains this well. Click here to read.

If you are selfish, and make yourself and your own private interests your idol, God will leave you to yourself, and let you promote your own interests as well as you can. But if you do not selfishly seek your own, but do seek the things that are Jesus Christ’s, and the things of your fellow-beings, then God will make your interest and happiness his own charge, and he is infinitely more able to provide for and promote it than you are. The resources of the universe move at his bidding, and he can easily command them all to subserve your welfare. So that, not to seek your own, in the selfish sense, is the best way of seeking your own in a better sense. It is the directest course you can take to secure your highest happiness. When you are required not to be selfish, you are not required, as has been observed, not to love and seek your own happiness, but only not to seek mainly your own private and confined interests. But if you place your happiness in God, in glorifying him, and in serving him by doing good, — in this way, above all others, will you promote your wealth, and honor, and pleasure here below, and obtain hereafter a crown of unfading glory, and pleasures forevermore at God’s right hand. If you seek, in the spirit of selfishness, to grasp all as your own, you shall lose all, and be driven out of the world at last, naked and forlorn, to everlasting poverty and contempt. But if you seek not your own, but the things of Christ, and the good of your fellowmen, God himself will be yours, and Christ yours, and the Holy Spirit yours, and all things yours. (Jonathan Edwards from "Charity and Its Fruits")