St. Thomas Aquinas:

described Spiritual Communion as:

“an ardent desire to receive Jesus in the Holy Sacrament and a loving embrace as though we had already received Him.”

Act of Spiritual Communion Prayer

My Jesus,

I believe that You are present in the Most Holy Sacrament.
I love You above all things, and I desire to receive You into my soul.
Since I cannot at this moment receive You sacramentally,

come at least spiritually into my heart.
I embrace You as if You were already there

and unite myself wholly to You.
Never permit me to be separated from You.

Amen.

Spiritual Communion

For When You Are Unable to Receive Communion

St. Jean-Marie Vianney:

“If we are deprived of Sacramental Communion, let us replace it, as far as we can, by spiritual communion, which we can make every moment; for we ought to have always a burning desire to receive the good God.”