What is a Spiritual Communion?
If someone for example is at Mass and is not able to receive the Eucharist because of not having an opportunity to confess a serious sin, or is a RCIA candidate, can at the time of Communion, ask Jesus to spiritually enter one's heart, embracing Jesus as if one had received Him sacramentally (i.e., an Act of Spiritual Communion).
In his encyclical letter, Ecclesia de Eucharistia, Pope John Paul II wrote the following:
The Eucharist thus appears as the culmination of all the sacraments in perfecting our communion with God the Father by identification with his only-begotten Son through the working of the Holy Spirit. With discerning faith a distinguished writer of the Byzantine tradition voiced this truth: in the Eucharist “unlike any other sacrament, the mystery [of communion] is so perfect that it brings us to the heights of every good thing: here is the ultimate goal of every human desire, because here we attain God and God joins himself to us in the most perfect union”. Precisely for this reason it is good to cultivate in our hearts a constant desire for the sacrament of the Eucharist. This was the origin of the practice of “spiritual communion”, which has happily been established in the Church for centuries and recommended by saints who were masters of the spiritual life. Saint Teresa of Jesus wrote: “When you do not receive communion and you do not attend Mass, you can make a spiritual communion, which is a most beneficial practice; by it the love of God will be greatly impressed on you”. (Paragraph 34 of Ecclesia de Eucharistia).
An Act of Spiritual Communion can also be made at Eucharistic Adoration, or if someone is at home and is unable to be at Mass because of a sickness.
I feel that it is important to remind all that an Act of Spiritual Communion must never replace going to Mass and receiving the Eucharist in a state of grace. The most powerful and intimate way Jesus can embraces us here on Earth, is to be at Mass and to receive the Blessed Sacrament.
Regarding prayers for spiritual communion, this Act of Spiritual Communion is found in the Sacred Apostolic Penitentiary’s Enchiridion of Indulgences:
My Jesus, I believe that you are in the Blessed Sacrament. I love you above all things, and I long for you in my soul. Since I cannot now receive you sacramentally, come at least spiritually into my heart. As though you have already come, I embrace you and unite myself entirely to you; never permit me to be separated from you. Amen.
According to the Enchiridion of Indulgences, one gains a partial indulgence by making an act of spiritual communion.