8 How, then, do we find the two precepts of love indicated in these two commands of the Lord? “Take up your bed,” says He, “and walk.” What the two precepts are, my brethren, recollect with me. For they ought to be thoroughly familiar to you, and not merely to come into your mind when they are recited by us, but they ought never to be blotted out from your hearts. Let it ever be your supreme thought, that you must love God and your neighbor: “God with all your heart, and with all your soul, and with all your mind; and your neighbor as yourself.”
These must always be pondered, meditated, retained, practised, and fulfilled. The love of God comes first in the order of enjoying; but in the order of doing, the love of our neighbor comes first. For He who commanded you this love in two precepts did not charge you to love your neighbor first, and then God, but first God, afterwards your neighbor. Thou however, as you do not yet see God dost earn to see Him by loving your neighbor; by loving your neighbor you purge your eye for seeing God, as John evidently says, “If you love not your brother whom you see, how can you love God, whom you do not see?” See, you are told, “Love God.”
If you say to me, “Show me Him, that I may love Him;” what shall I answer, but what the same John says: “No man has seen God at any time”? And, that you may not suppose yourself to be wholly estranged from seeing God, he says, “God is love; and he that dwells in love dwells in God.” Therefore love your neighbor; look at the source of your love of your neighbor; there you will see, as you may, God. Begin, then, to love your neighbor. “Break your bread to the hungry, and bring into your house him that is needy without shelter; if you see the naked, clothe him; and despise not those of the household of your seed.”
And in doing this, what will you get in consequence? “Then shall your light break forth as the morning light.” Your light is your God, a “morning light” to you, because He shall come to you after the night of this world: for He neither rises nor sets, because He is ever abiding. He will be a morning light to you on your return, He who had set for you on your falling away from Him. Therefore, in this “Take up your bed,” He seems to me to have said, Love your neighbor.
Source: Tractates on the Gospel of John (New Advent)