The rich young man approached Jesus and asked (according to a variant text, which I prefer), "Teacher, what good thing shall I do that I may have eternal life? So He said to him, Why do you ask me about what is good? There is One Who is good. But if you want to enter into life, keep the commandments." Then the young man asked (as though he did not already know), "Which ones?" Christ thereupon recites five of the ten--as though to jog the man's memory. "Oh, those commandments," he might have said. "Of course I have kept them... since I was a child. But there's got to be more than that. So... what do I still lack?"
You see, following the letter of the Law--while never easy--is doable. Even the Pharisees could boast that they were faithful followers of the Law, carefully observing the traditions of their fathers down to the smallest detail. (Of course they did this in a spirit of pride, and thus unto their own condemnation). Beyond this fact, however, they missed the point: the Law revealed unto Moses was never intended to be an end in itself. It is rather a means through which we express our humble and willing obedience to God and our sincere desire to live our lives according to His precepts.
Jesus says that if we desire to enter into life, it is necessary first of all that we keep the commandments. He does not say that our merely outward keeping of the Law guarantees our salvation. Because there are no guarantees--though this is what the rich man seems to have been searching for. The truth is, we can only enter into the eternal life of God's Kingdom when we are willing to relinquish our own life in this world in a spirit of sacrificial love. If we desire to save our soul, we must lose it--that we may say with St. Paul, "It is no longer I who live, but Christ in me."
Therefore our Lord tells the young man, "If you would be perfect, go, sell what you have, and give to the poor, and you will have treasure in heaven; and come follow me." And why?.... Because the man was holding back, just as you and I are tempted to do. "I will do anything for the sake of my Lord and Savior," we may well say, "except...." Consider the example of Ananias and Sapphira in the Book of Acts, who held back a portion of the money they had pledged to the Church (and ended up paying for this sin with their lives). There is almost always an exclusionary clause in our "contract" with God.
But in terms of our relationship with God, it has got to be all or nothing. He commands that we must love Him with all of our heart, soul and mind and our neighbor as our very own self. And while this is indeed a standard most of us fall far short of, let us at least strive to attain it according to the grace God has given us, always remembering Christ's words: "With men this is impossible, but with God all things are possible."