"FOLLOWING after God is the desire of happiness; to reach God is happiness itself. We follow after God by loving Him; we reach Him, not by becoming entirely what He is, but in nearness to Him, and in wonderful and immaterial contact with Him, and in being inwardly illuminated and occupied by His truth and holiness. He is light itself; we get enlightenment from Him. The greatest commandment, therefore, which leads to happy life, and the first, is this: "You shall love the Lord your God with all your heart, and soul, and mind." For to those who love the Lord all things issue in good. Hence Paul adds shortly after, "I am persuaded that neither death, nor life, nor angels, nor virtue, nor things present, nor things future, nor height, nor depth, nor any other creature, shall be able to separate us from the love of God, which is in Christ Jesus our Lord." (Rom 8:38-39) If, then, to those who love God all things issue in good, and if, as no one doubts, the chief or perfect good is not only to be loved, but to be loved so that nothing shall be loved better, as is expressed in the words, "With all your soul, with all your heart, and with all your mind," who, I ask, will not at once conclude, when these things are all settled and most surely believed, that our chief good which we must hasten to arrive at in preference to all other things is nothing else than God? And then, if nothing can separate us from His love, must not this be surer as well as better than any other good?"
~St. Augustine: De Moribus Ecclesiae Catholicae, Chap. 11.