The further you go in the revealed thoughts of God, the clearer you see that God's aim in creating the world was to display the value of his own glory.
John PiperThere is a warning. The path of God-exalting joy will cost you your life. Jesus said, “Whoever loses his life for my sake and the gospel’s will save it.” In other words, it is better to lose your life than to waste it. If you live gladly to make others glad in God, your life will be hard, your risks will be high, and your joy will be full. This is not a book about how to avoid a wounded life, but how to avoid a wasted life. Some of you will die in the service of Christ. That will not be a tragedy. Treasuring life above Christ is a tragedy.
John PiperTherefore bread was created for the glory of Christ. Hunger and thirst were created for the glory of Christ. And fasting was created for the glory of Christ. Which means that bread magnifies Christ in two ways: by being eaten with gratitude for his goodness, and by being forfeited out of hunger for God himself. When we eat, we taste the emblem of our heavenly food—the Bread of Life. And when we fast we say, “I love the Reality above the emblem.” In the heart of the saint both eating and fasting are worship. Both magnify Christ.
John PiperSo saving grace, converting grace, for Augustine, is God's giving us a sovereign joy in God that triumphs over all other joys and therefore sways the will. The will is free to move toward whatever it delights in most fully, but it is not within the power of our will to determine what that sovereign joy will be.
John Piper