It is the Eucharist that fulfills this meaning of sacramental mysticism. It is here that we encounter Christ truly, really, and substantially present to us. It is food that nourishes our spirit, that eternal wisdom. Thus, the sacraments, especially the Eucharist, give us the ability to respond to God's love to us. God gives Himself to us in the Eucharist, in which we respond back in praise and thanksgiving through the contemplation of that which we just received, through the contemplation of the Divine Mystery of God's love. This brings us to many realizations about the Eucharist. First and foremost, the Eucharist is something we receive, we do not take. The Eucharist is God's gift to us, and the priest stands there in the person of Christ, thus Christ is giving Himself to us, just as He gave Himself to the Apostles 2000 years ago. As a result of this gift, we exclaim Amen(and it ought to be a joyful exclamation)! Amen means “Let it be so, It is True, I believe”. That is our response to the gift of Christ. Thus, in the Eucharist we experience God's love in its threefold fullness. We receive the healing power of the Eucharist through the grace we receive which helps us grow closer to God in the forgiveness of our sins, hence the inseparability of the Sacrament of the Eucharist from the Sacrament of Reconciliation. Without one, there would not be the other. Secondly, God seeks us out first. The priest says “The body of Christ”. Christ has come to seek us out and make Himself known to us, and presents Himself to us through the priest. Thirdly, God gives Himself to us completely in the Eucharist. We witness the sacrifice of Christ in the Mass which makes God present to us, and we receive that ultimate love, Christ, from that ultimate act of love, His death on the Cross.
That is only the aspect of God's action of love in the Eucharist, we have a loving aspect as well. We go up to receive the Eucharist. We go out to seek God. Our hearts yearn for that truth which is made present to us in the Eucharist, it is what we truly long for and yet, it is something we cannot attain on our own. Thus God comes down to us so that we may receive His love. God gives Himself to us when we seek Him, because He seeks us first. When it comes time for us to have the privilege of receiving our Lord in the Blessed Sacrament, we make some sort of act of worship before reception. This is that outward sign of that interior reality. We have faith that what we are to receive is Christ, and we make that know by bowing, genuflecting, or making the sign of the Cross. This is our act of love to God, acknowledging Him for Who He is. Then the priest says “The Body of Christ” and we say Amen. We thus give ourselves over to God through that act of faith made known through our exclamation of Amen! Thus, love between man and God is comes to it fullness in the Eucharist. We participate in that heavenly reality right now and thus also have a foreshadowing of what Heaven will truly be like. The liturgy is an experience of Heaven, and Heaven, as is experienced through the liturgy, is a communion of love between God and His creation. There is much, MUCH more to say on this aspect of the encyclical, but that could take nights up nights to discuss. I highly recommend you go out and read it for yourself to see these truths which our Pope speaks of with regards to the Eucharist.