St. Alphonsus Liguori
“As in all the following visits to the Most Blessed Sacrament a spiritual communion is recommended, it will be well to explain what it is, and the great advantages which result from its practice. A spiritual communion, according to St. Thomas, consists in an ardent desire to receive Jesus in the Most Holy Sacrament, and in lovingly embracing Him as if we had actually received Him. How pleasing these spiritual communions are to God, and the many graces which He bestows through their means.”
Source: St. Alphonsus Liguori, Visits to the Most Holy Sacrament