Fr. Michael Mueller's book, the Blessed Eucharist, our greatest treasure, is a work of priceless value for us teaching us the inconceivable and inestimable blessing that is this Mystery of Infinite Love. But since in these times, some may object it is difficult to receive Sacramental Communion daily or frequently, the chapter especially on Spiritual Communions is worth reading and re-reading.

We should make Spiritual Communions many times a day, and depending on the intensity of our love, and the burning desire of our heart to be united with the Savior's Sacred Heart, to make reparation to Him for sins, and to attain union with Him, we can receive graces comparable or at times even almost equal to those which we would receive by Sacramental Communion. Let our whole day, nay, our whole lives, be a continual preparation, participation and thanksgiving for this precious Sacrament of Divine Love. Let us often strive to participate at the Holy Traditional Latin Mass as frequently as we can. But let not our zeal grow cold or our hearts grow weary if, owing to circuмstances beyond our control, we cannot communicate Sacramentally very often. Those days especially, we must develop the habit of preparing and disposing ourselves to receive Our Lord's Presence in spiritual communions many times a day.

http://www.catholictradition.org/Eucharist/blessed-eucharist11.htm

CHAPTER 11
On Spiritual Communion

WHEN a soul has once begun to practice frequent Communion, she can no longer live without it.

Even if she were to communicate every day, it would seem too little. She would desire, if possible, to receive Our Lord every moment. It is the Blessed Sacrament itself which produces this effect, for such is the sweetness of that Divine Food that they that eat it hunger still and they that drink it thirst again. It is Our Lord Himself who excites this desire in the hearts of the faithful, and He also has provided a means of satisfying it. While He was yet on earth, He not only imparted many graces to those who were near Him, but He also wrought many miracles in behalf of those who were at a distance.
In like manner, He now not only bestows many graces upon us when He actually enters our hearts in Holy Communion, but He also imparts many to us by means of Spiritual Communion. St. Catherine of Siena, while on one occasion assisting at the Mass of her confessor, St. Raymund, felt the most ardent desire to be united to Jesus Christ; but as she had been forbidden to communicate, she did not dare to receive. Our Lord, however, was so moved by the fervor of her love that He worked a miracle in her favor. At that part of the Mass in which the priest breaks the Sacred Host into three pieces, the smallest portion disappeared from the altar, flew through the air and rested upon the tongue of St. Catherine. St. Raymund was much disturbed at the disappearance of the particle, but the Saint relieved his anxiety by telling him that Our Lord Himself had been pleased to communicate her in reward for her great desire for Holy Communion. He displays a similar love towards everyone who has a true desire to be united to Him. As soon as a soul ardently desires to receive Our Lord in the Blessed Sacrament, He comes to satisfy her desire, not indeed as He did to St. Catherine under the Sacramental species, but by the way of Spiritual Communion. This devotion is so full of grace and consolation that it is of the greatest importance that everyone should know how to practice it. I will therefore say a word in explanation of it.

Spiritual Communion, according to St. Thomas, consists in an ardent desire to receive our Lord Jesus Christ in the Most Holy Sacrament. It is performed by making an act of faith in the presence of Jesus Christ in the Blessed Sacrament, and then an act of love, and an act of contrition for having offended Him. The soul then invites Him to come and unite Himself to her and make her entirely His own; and lastly, she thanks Him as if she had really received Him sacramentally.

The Spiritual Communion may be made in the following manner: "O my Jesus, I firmly believe that Thou art truly and really present in the Most Holy Sacrament. I love Thee with my whole heart, and because I love Thee, I am sorry for having offended Thee. I long to possess Thee within my soul, but as I cannot now receive Thee sacramentally, come at least in spirit into my heart. I unite myself to Thee as if Thou wert already there; never let me be separated from Thee."

The graces which are bestowed in this way are so great that they may be likened to those which are imparted by an actual reception of the Sacrament.

One day Our Lord Himself told St. Jane of the Cross that as often as she communicated spiritually she received a grace similar to that which she received from her Sacramental Communions. He also appeared to Sister Paula Maresca, foundress of the Convent of St. Catherine of Siena at Naples, with two vessels, one of gold and the other of silver, and told her that in the golden vessel He preserved her Sacramental Communions and in the silver vessel her spiritual Communions. The Fathers of the Church go so far as to say that one who has a very great desire for Communion, accompanied with great reverence and humility, may sometimes receive even more graces than another who, without these dispositions, should actually receive Our Lord in the Sacramental species; for as the Psalmist says: "The Lord hears the desire of the poor, and fills their hearts with good things."

The advantages of this mode of Communion are very great. To practice it, you will not need to go to church or make a long preparation or remain fasting; you will not need to ask the permission of your confessor, or to seek a priest to give it to you as in Holy Communion. Hence, the venerable Jane of the Cross used to say: "O my Lord, what an excellent mode of receiving without being seen or remarked, without giving trouble to my spiritual father, or depending on anyone but Thee, who in solitude dost nourish my soul and speak to my heart."

But the chief advantage of Spiritual Communion is that it may be so often repeated. You can receive Sacramental Communion at most but once a day, but Spiritual Communion you may receive as often as you please. St. Alphonsus advises one who wishes to lead a devout life to make Spiritual Communions at his meditations, at his visits to the Blessed Sacrament and whenever he hears Mass. But especially he should endeavor to multiply them on the eve of his Communions because, as Father Faber of the Society of Jesus remarks, they are most powerful means to attain the dispositions necessary for a good Communion. The Saints were much addicted to this devotion.

The Blessed Angela of the Cross, a Dominican nun, was accustomed to make a hundred Spiritual Communions every day and a hundred more every night, and she used to say: "If my confessor had not taught me this method of communicating, I could scarcely live." If you ask how she could make so many, I answer with St. Augustine: "Give me a lover, and he will understand; give me a soul that loves nothing but Jesus Christ, and she will know how to do it."