Secret #7 of Vinny Flynn's 7 Secrets of the Eucharist is about spiritual communion. It may be my favorite part of his book. I wanted to highlight some of the sources he quotes which I found the most meaningful.
Sacramental Communion brings us into union with God, and spiritual Communion helps keep us there (pp. 88-89).
He quotes a vision of St. Catherine of Siena, where Jesus is holding two chalices:
In this golden chalice I put your sacramental communions. In this silver chalice I put your spiritual communions. Both chalices are quite pleasing to me (p. 89).
Flynn quotes St. Padre Pio:
In the course of the day,...call on Jesus, even in the midst of all your occupations.... He will come and will remain always united with your soul by means of His grace and His holy love.
Fly with your spirit before the tabernacle, when you cannot stand before it bodily, and there pour out the ardent longings of your soul and embrace the Beloved of souls, even more than if you had been permitted to receive Him sacramentally (p. 91).
He gives the prayer for spiritual communion from St. Alphonsus Liguori:
My Jesus, I believe that you are really present in the Most Holy Sacrament. I love you above all things, and I desire to possess you sacramentally, come at least spiritually into my heart. I embrace you as being already there and unite myself wholly to you. Never permit me to be separated from you (p. 95).
Flynn talks about some of the wordless images he uses for spiritual communion. I especially like his image of Mary visiting him as she did Elizabeth in the Visitation, but bringing her Son into Flynn's heart.
Someone who engaged in nearly continuous spiritual communion was Brother Lawrence, a 17th-century French Carmelite whose Practice of the Presence of God talks about how he did this:
That we should establish ourselves in a sense of God's presence by continually conversing with Him. That it was a shameful thing to quit His conversation to think of trifles and fooleries.
More on Brother Lawrence later.