St. Francis wrote abundantly on the Holy Eucharist.
Here is a sample of his thoughts, for your reflection
“The Holy Eucharist is the perfect Communion of Saints, for it is the food common to angels, and sainted souls in Paradise, and ourselves; it is the true bread of which all Christians participate. The forgiveness of sins, the author of forgiveness being there, is confirmed; the seed of our resurrection sown, life everlasting bestowed. … This very belief in the most holy Sacrament, which in truth, reality, and substance, contains the true and natural body of Our Lord, is actually the abridgment of our faith, according to that of the Psalmist “He had made a memory of his wonderful works.” O holy and perfect memorial of the Gospel! O admirable summing up of our faith! He who believes, O Lord, in your presence in this most holy sacrament, as your holy Church proposes it, has gathered and sucked the sweet honey of all the flowers of your holy religions: hardly can he ever fail in faith. (Catholic Controveries 324)
(God will fulfill all his) divine promises in a surprising manner. “I will lead her into the wilderness, and I will speak to her heart, and I will give her milk.” “Rejoice with Jerusalem and be glad with her that you may draw out milk and be filled at the breasts of her consolation, that you may suck and find delight at all the abundance of her glory. You shall be carried at the breasts, and upon their knees they shall caress you.”
Such is infinite happiness and it has not only been promised to us but we have a pledge of it in the most holy sacrament of the Eucharist, the perpetual feast of divine grace. In it we receive our Savior’s blood in his flesh and his flesh in his blood, for his blood is dispensed to us by his flesh, his substance by his substance. It is given into our bodily mouths so that we may know that he will give us his own divine essence in an eternal feast of glory. Here on earth, it is true, this boon is granted to us really but in a hidden way, under sacramental species and appearances, whereas in heaven, God will give himself openly and “we shall see him face to face, as he is.” Treatise on the Love of God 1, 3: 11, 191-92
The holy love of the Savior presses us, said St. Paul. O God, what an example of surpassing union is this! God was united to our human nature by grace, like a vine to an elm, to enable it in some way to participate in his fruit. But when he saw this union undone by Adam’s sin, he made a closer and more pressing union in the Incarnation and by it human nature remains forever joined in personal unity with the divinity. To the end that not only human nature but all men might be intimately united with his goodness, God instituted the sacrament of the most holy Eucharist. Every man may participate in it so as to unite his Savior with himself in reality and in the way of food. This sacramental union calls us and assists us towards that spiritual union of which we speak (Treatise on the Love of God 2, 7:2, 20-21)
Our Savior has instituted the most August sacrament of the Eucharist, which contains His Flesh and His Blood in their reality, to the end that he who eats of it shall live forever. Whoever, therefore, frequently eats with devotion this food, so effectually confirms the health of his soul that it is almost impossible that he should be poisoned by any kind of evil affection. We cannot be nourished with this flesh of life and at the same time live with the affections of death. Thus, as men dwelling in the earthly paradise might have avoided corporal death by power of that living fruit which God had planted therein, so they may also avoid spiritual death by virtue of this sacrament of life.”
Introduction to the Devout Life 2:20