Why Doesn't the Eucharist Change Everyone's Life?

About 6 years ago, I was sharing with an evangelical friend about the life-changing properties I had discovered in the Eucharist. I had just come into the Catholic Church and was so excited to experience the grace God has for us in this Blessed Sacrament. He then asked me, "If the Eucharist is so life-changing as you say, why then are there many Catholics who go up for Communion every week not changed?"
       I didn't really know how to answer him at the time but have thought about that question many times over the past few years. Particularly in my own life. How could I have been a young long-haired Catholic kid playing guitar in the folk Mass on Sunday receiving the Eucharist, but smoking pot and breaking the law the night before? Why didn't the grace in the Eucharist I was receiving change me or wake me up to see the hypocrisy in my life? This scripture from the gospel of Mark recently gave me an inkling of an answer to this question.

"A large crowd followed and pressed around him. 25 And a woman was there who had been subject to bleeding for twelve years. 26 She had suffered a great deal under the care of many doctors and had spent all she had, yet instead of getting better she grew worse. 27 When she heard about Jesus, she came up behind him in the crowd and touched his cloak, 28 because she thought, "If I just touch his clothes, I will be healed." 29 Immediately her bleeding stopped and she felt in her body that she was freed from her suffering.
30 At once Jesus realized that power had gone out from him. He turned around in the crowd and asked, "Who touched my clothes?"
31 "You see the people crowding against you," his disciples answered, "and yet you can ask, 'Who touched me?' "
32 But Jesus kept looking around to see who had done it. 33 Then the woman, knowing what had happened to her, came and fell at his feet and, trembling with fear, told him the whole truth. 34 He said to her, "Daughter, your faith has healed you. Go in peace and be freed from your suffering."

Many were crowding around Jesus and even touching Him, yet he perceived that it was one particular woman's faith that lead to the release of His grace and her healing. The many other people crowding around him that day may have been just "going through the motions" following the crowd that day. Perhaps the grace received in the Eucharist is similar. When an individual receives Christ's body and blood but is indifferent, perhaps not even believing, they are not cooperating with God's grace, and hence will not receive the grace.
As St Paul said, it is so vitally important to properly discern the body of Christ at the Lord's Table. Christ works through His sacraments to the degree that we are open and docile to His work. The saints through the ages have written volumes on how to prepare one's heart to receive the Eucharist. So it comes down to our willingness to cooperate with grace of God. Many receive the Eucharist with no intention of cooperating with God. They may even be in mortal sin, God forbid, as I once was as a rebellious young adolescent. Perhaps they are just going through the motions, like some of the folks in the crowd that day. They were just carried along by the momentum of the crowd, but weren't sure who it was they were getting near nor understood what He was offering to them. And so it is with the Eucharist.
  (this is an edited version of a  post I wrote in 2008)