"Christ is the seal on the forehead, the seal on the heart: on the forehead, that we may ever confess him: on the heart, that we always love him; a seal on the arm, that we may carry out his tasks.
"Therefore, let his image radiate in our confession, let it radiate in our love, let it radiate in our works and deeds, so that all his beauty may be expressed in us if it is possible. Let him be our head, because 'the head of everyone is Christ.' Let him be our eye, that through him we may see the Father. Let him be our voice, that through him we may speak to the Father. Let him be our right hand, that through him we may bring our sacrifice to God the Father. He is also our seal, which is the sign of perfection and love, because the Father loved the Son and set his seal on him, as we read: 'It is on him that God the Father has set his seal.'
"Therefore, Christ is our love. Love is good, when it has remitted sins. Hence, let our soul put on love, a kind of love which is as 'strong as death.' For just as death is the end of sins, so is love as well, since the person who loves the Lord ceases to commit sin." (Ambrose, Bishop of Milan, "Treatise on Isaac or the Soul"; cited in Wright, Readings for the Daily Office from the Early Church, p. 95)