She prayed this prayer to express the desire she had for Jesus to dwell within her heart.
St. Elizabeth Ann Seton was raised as an Episcopalian and converted to Catholicism as an adult, witnessing the beauty and wonder of the Catholic faith. In particular, she was drawn to the Eucharist and was eager to receive Jesus Christ within her heart.
Here is a short prayer she wrote down that fostered that longing she had for the Eucharist, desiring Jesus to come to her in communion.
O, food of Heaven, how my soul longs for you with desire! Seed of Heaven, pledge of its immortality, of that eternity it pants for. Come, come my Jesus, bury yourself within this heart. It shall do its best to preserve that warmth which will bring forth the fruits of eternity. O, Amen. Our Jesus.