why did Christ institute this Sacrament of His Body and Blood?

St. Teresa says that Christ is disguised as bread so that we will not fear to approach Him – so that we can go to Him in confidence, daily, needing Him as we need our physical bread.
We are not, most of us, capable of exalted emotion, save rarely. We are not capable always of feelings of love, awe, gratitude, and repentance. So Christ has taken the form of bread that we may more readily approach Him, and feeding daily, assimilating Christ so that it is not we but Christ working in us, we may be made more capable of understanding and realizing and loving Him.
Yes, in bread Christ has become so simple – has condescended so far, that a child can eat the Sacred Food with love and gratitude. He said that we would be scandalized, so it is no use for me to be surprised and horrified at the bluntness of your objection. Even the nearest and dearest of His friends dispersed and fled, not realizing the mystery of the Redemption, that Christ was laying down His life for all men.
When He prayed in agony in the garden – when the weight of our sins descended upon Him, all the sins that had been and that would be committed throughout the world forever, after; when He suffered all the temptations, all the horror, all the remorse for the rest of the world – His disciples did not understand that either. He watched and suffered alone in His agony. He had told them that the next day He was to die. And in spite of His miracles they paid so little attention to His words that they slept, as the Friend they loved most in the world struggled against the thought of His death. They left Him alone, they slept, and the next day they fled, so little did they understand His teachings, though they had been with Him for three years. They did not understand even after they had eaten with Him at the Last Supper. They did not understand until the Holy Spirit descended upon them and it was given them to understand.
So how can I understand or try to tell you about it? If they who lived with Him, who could see Him as man, eat with Him, sleep with Him, and wander with Him through the countryside, if they were “offended” and dispersed, how can I try to tell you what is in my heart? I do not ask myself, “How can I try to overcome your objection?’ Only God can do that. I am not trying to convert you, but just trying not to let go unchallenged your objections, for fear that my not answering would seem to you a kind of denial of Him Whom I love.
There is the question, why did Christ institute this Sacrament of His Body and Blood? And the answer is very simple. It was because He loved us and wished to be with us. “My delights are to be with the children of men.” He made us and He loves us. His presence in the Blessed Sacrament is the great proof of that love.

By Dorothy Day, from her book From Union Square to Rome, pages 164 -166.