Here is another approach that came to me while I was at daily Mass about fifteen minutes ago.
During Holy Communion, we are invited to become one with Christ. His very self enters us in a unique and profound manner as we receive Him in Holy Communion. Jesus wants to touch us and embrace us, body to body. During the homily that he preached at his first World Youth Day Mass, Pope Benedict XVI took this a rather shocking step further:
We can only fully accept it when we take the second step that the Last Supper proposes to us. The Latin word for adoration is ad-oratio - mouth to mouth contact, a kiss, an embrace, and hence, ultimately love. Submission becomes union, because he to whom we submit is Love. In this way submission acquires a meaning, because it does not impose anything on us from the outside, but liberates us deep within.
This is the kind of union that Jesus proposes to us as we form the line to receive Him in Holy Communion. It is the most profound union that we can undertake with God, Himself.
We are invited, at the “Ecce Agnus Dei” to touch God and to receive Him (either on the tongue or in the hand) and allow Him to enter our bodies. We become one with Him.
That is the reason why we form a line. That is why the Church calls this the “Communion” procession.
Lamentably, there are those who, for whatever reason, cannot receive our Lord in Holy Communion. That is why the Church, in her great solicitude, offers these individuals the chance to make a spiritual Communion where they can ask Jesus to enter into their hearts spiritually, as they kneel at their pews.
A blessing in lieu of receiving Holy Communion obviously cannot achieve that same union. A blessing is a blessing. The Church designates a specific time for this to occur, at the end of the Holy Sacrifice of the Mass. Everyone will receive that blessing.