What is a spiritual Communion?
A spiritual Communion is our reception of Our Lord Jesus Christ into our hearts at that moment when we are unable to receive Him sacramentally.
What is the value of such a practice?
Now for the surprise, in making a spiritual Communion, it is possible to receive more graces than with an actual reception of Holy Communion. How can this be? While of course the act of receiving Jesus under the Sacramental veils carries with it the possibility of enough grace to save ones soul, we are always under-preparred for such a wonderful occasion. Would that this be all that was lacking (perfection of intention) when we received Jesus in Holy Communion. Unfortunately, more often than not, we neglect preparing altogether or do not prepare sufficiently as can be done in our state in life. In this way we do not receive the full "grace potential" from a reception of the Most Blessed Sacrament. When we make a spiritual Communion however, we frequently spend a few minutes or perhaps longer in anticipation and a few minutes in thanksgiving. THE GRACES ABOUND!
I do not recall at the moment which saint said this but it has been recommended that after receiving Holy Communion, a spiritual Communion be made immeadiately so that the fire of love in your hearts does not die out as it has just received That which it longed for. This is a wonderful practice that I can personally endorse as having done wonders for my love for the Holy Eucharist.
How is a spiritual Communion made?
There is no specific or required formula for a spiritual Communion. The prayer can be made up on the spot by the person seeking the spiritual Communion. Here are a number of spiritual Communion ideas, take and mold these together or add your own bits and pieces to make it something for you! Here are three examples, the first from St. Alphonsus.
Act of Spiritual Communion by St. Alphonsus Liguori (A.D. 1696-1787)
My Jesus, I believe that Thou art present in the Blessed Sacrament. I love Thee above all things and I desire Thee in my soul. Since I cannot now receive Thee sacramentally, come at least spiritually into my heart. As though thou wert already there, I embrace Thee and unite myself wholly to Thee; permit not that I should ever be separated from Thee.
O Immaculate Queen of Heaven and Earth, Mother of God and Mediatrix of every grace: I believe that Thy dearly beloved Son, Our Lord Jesus Christ, is truly, really, and substantially contained in the Most Blessed Sacrament. I love Him above all things and I long to receive Him into my heart. Since I cannot now receive Him sacramentally, be so good as to place Him spiritually in my soul. O my Jesus, I embrace Thee as One who has already come, and I unite myself entirely to Thee. Never permit me to be separated from Thee.
As I cannot this day enjoy the happiness of assisting at the holy Mysteries, O my God! I transport myself in spirit at the foot of Thine altar; I unite with the Church, which by the hands of the priest, offers Thee Thine adorable Son in the Holy Sacrifice; I offer myself with Him, by Him, and in His Name. I adore, I praise, and thank Thee, imploring Thy mercy, invoking Thine assistance, and presenting Thee the homage I owe Thee as my Creator, the love due to Thee as my Savior. Apply to my soul, I beseech Thee, O merciful Jesus, Thine infinite merits; apply them also to those for whom I particularly wish to pray. I desire to communicate spiritually, that Thy Blood may purify, Thy Flesh strengthen, and Thy Spirit sanctify me. May I never forget that Thou, my divine Redeemer, hast died for me; may I die to all that is not Thee, that hereafter I may live eternally with Thee. Amen.
It is not unheard of to pray the "Lord I am not worthy" prayer once or three times as is done during Mass before the silence and contemplation after the petition to Our Lord.