From the Tractates on the first letter of John by Saint Augustine, bishop
Our heart longs for God
We have been promised that we shall be like him, for we shall see him as he is. By these words, the tongue has done its best; now we must apply the meditation of the heart. Although they are the words of Saint John, what are they in comparison with the divine reality? And how can we, so greatly inferior to John in merit, add anything of our own? Yet we have received, as John has told us, an anointing by the Holy One which teaches us inwardly more than our tongue can speak. Let us turn to this source of knowledge, and because at present you cannot see, make it your business to desire the divine vision.
The entire life of a good Christian is in fact an exercise of holy desire. You do not yet see what you long for, but the very act of desiring prepares you, so that when he comes you may see and be utterly satisfied.
Suppose you are going to fill some holder or container, and you know you will be given a large amount. Then you set about stretching your sack or wineskin or whatever it is. Why? Because you know the quantity you will have to put in it and your eyes tell you there is not enough room. By stretching it, therefore, you increase the capacity of the sack, and this is how God deals with us. Simply by making us wait he increases our desire, which in turn enlarges the capacity of our soul, making it able to receive what is to be given to us.
So, my brethren, let us continue to desire, for we shall be filled. Take note of Saint Paul stretching as it were his ability to receive what is to come: Not that I have already obtained this, he said, or am made perfect. Brethren, I do not consider that I have already obtained it. We might ask him, “If you have not yet obtained it, what are you doing in this life? This one thing I do, answers Paul, forgetting what lies behind, and stretching forward to what lies ahead, I press on toward the prize to which I am called in the life above. Not only did Paul say he stretched forward, but he also declared that he pressed on toward a chosen goal. He realized in fact that he was still short of receiving what no eye has seen, nor ear heard, nor the heart of man conceived.
Such is our Christian life. By desiring heaven we exercise the powers of our soul. Now this exercise will be effective only to the extent that we free ourselves from desires leading to infatuation with this world. Let me return to the example I have already used, of filling an empty container. God means to fill each of you with what is good; so cast out what is bad! If he wishes to fill you with honey and you are full of sour wine, where is the honey to go? The vessel must be emptied of its contents and then be cleansed. Yes, it must be cleansed even if you have to work hard and scour it. It must be made fit for the new thing, whatever it may be.
We may go on speaking figuratively of honey, gold or wine—but whatever we say we cannot express the reality we are to receive. The name of that reality is God. But who will claim that in that one syllable we utter the full expanse of our heart’s desire? Therefore, whatever we say is necessarily less than the full truth. We must extend ourselves toward the measure of Christ so that when he comes he may fill us with his presence. Then we shall be like him, for we shall see him as he is.