Thomas Aquinas (1225-1274)

This is what happens by divine power in this sacrament; for the whole substance of bread is converted into the whole substance of the body of Christ, and the whole substance of wine into the whole substance of the blood of Christ. Hence this conversion is not formal, but substantial; nor is it contained within the categories of natural motion, but may be called by its proper name, transubstantiation.

Teresa of Avila (1515-1582)

In the presence of Jesus in the Holy Sacrament we ought to be like the Blessed in heaven before the Divine Essence.

Odo Casel (1886-1948)

When we go with Christ in his way he becomes contemporary with us. He is neither past nor to come but present to us; he is always with us. And not only his person but also his saving act belongs to this present. There can be no deeper communion of living than that we should share the essential life and action of another.

Constitution on the Sacred Liturgy (Vatican II)

...the liturgy is the summit toward which the activity of the Church is directed; at the same time it is the fountain from which all her power flows.

Catechism of the Catholic Church

1325. The Eucharist is the efficacious sign and sublime cause of that communion in the divine life and that unity of the People of God by which the church is kept in being. It is the culmination both of God's action sanctifying the world in Christ and of the worship men offer to Christ and through him to the Father in the Holy Spirit.
1396. Those who receive the Eucharist are united more closely to Christ. Through it Christ unites them to all the faithful in one body--the Church. Communion renews, strengthens, and deepens this incorporation into the Church, already achieved by Baptism. In Baptism we have been called to form but one body. The Eucharist fulfills this call: "The cup of blessing which we bless, is it not a participation in the blood of Christ? The bread which we break, is it not a participation in the body of Christ? Because there is one bread, we who are many are one body, for we all partake of the one bread" (1 Cor 10: 16-17).
1404. The Church knows that the Lord comes even now in his Eucharist and that he is there in our midst. However, his presence is veiled. Therefore we celebrate the Eucharist "awaiting the blessed hope and the coming of our savior, Jesus Christ, asking to share in your glory when every tear will be wiped away. On that day we shall see you, our God, as you are. We shall become like you and praise you forever through Christ our Lord.

Mother Teresa of Calcutta (1910-1997)

The humility of Jesus can be seen in the crib, in the exile of Jesus, in the inability to make people understand him, in the desertion of his apostles, in the hatred of his persecutors, in all the terrible suffering and death of his passion, and now in his permanent state of humility in the tabernacle, where he has reduced himself to such a small particle of bread that the priest can hold him with two fingers. The more we empty ourselves, the more room we give God to fill us.

When you look at the crucifix, you understand how much Jesus loved you then. When you look at the Sacred Host you understand how much Jesus loves you now.