The thing you do not understand is the elemental fact that our beginning and our last end is God. Once that fact is accepted, half the struggle is won. If we wish to go on struggling, not to be content with the minimum of virtue, of duty done, of "just getting by," then we should account it a great honor that God has given us these desires, to serve Him and to use ourselves completely in His service.[snip. And I'm going to emphasize this bit as Pritcher did too.]
You do not see this, you do not believe it. Every now and then, when you think of religion in your busy life, you end by turning from it with aversion. You are young, and you have not yet really felt the need, the yearning toward God. You have not been in such agony and misery that you turned to One whom you knew not and said, "God help me!" Or if you did, you were ashamed of doing it afterward, feeling it to be cowardice to turn in misery to a God in Whom you did not believe.
St. John of the Cross, who lived at the same time as St. Teresa and was her good friend, tells about the different stages of prayer and how the first state is the purgative state. He explains how though we feel this joy and this longing of God, a joy which is so sweet that even the remembrance of it is a constant spur to us, still our own imperfections give us constant suffering and unease, and the struggle for the spiritual life is a wearisome one, and that we must not expect to find ease in prayer. He makes us understand this distaste, this recoil from religion. This lethargy comes from a consciousness of the imminence of the struggle, the fact that it is unceasing and will go on to death, and we often think that sheer thoughtless paganism would be a relief.