"Man lacks something. His sin has moved him away from the place where he should and could stand... He must make himself so light that grace outweighs everything else in him. He must forget himself - this is the only true conclusion that follows from the recognition of his nothingness - in order to allow grace to stream into the empty space that he is."
Our Christian faith teaches us that human beings originally existed in a state of grace, which state was lost because of sin, something recapitulated in all of our lives. Further, we know that sin is possible because we are created by Love in order to love and that genuine love, which we in the Latin tradition know as caritas, requires authentic freedom. Hence, in and through the waters of baptism God restores us to our original state. As St. Paul writes, specifically in chapters seven and eight of his Letter to the Romans, the hold of sin on us is very great: "For the good that I will to do, I do not do; but the evil I will not to do that I practice" (Romans 7:19). For this reason God sent "His only Son in the likeness of sinful flesh, on account of sin: He condemned sin in the flesh that the righteous requirement of the law might be fulfilled in us who do not walk according to the flesh but according to the Spirit" (Rom. 8:3-4).
So, we must empty ourselves in order to be filled with grace, which is nothing other than God's sharing divine life with us, the life that is life, which is nothing other than the life of the Most Blessed Trinity.