This Middle English poem was written in 15th-century handwriting, so that is the latest it could have been written. The Latin lines that provide the epigram were very common in English devotional writing of the Late Middle Ages. I strove to retain as many of the original words (with modernized spelling) as possible, though I did change the common merciable to merciful.
In cruce sum pro te, qui peccas; desine, pro me, Desine; do veniam; dic culpam, retraho penam.
On the Cross I am for you, who sin; desist, for Me, Desist; I give pardon; speak fault, I will withdraw penalty.
“Upon a cross nailed I was for thee, Suffered death to pay thy ransom; Forsake thy sin for the love of Me, Be repentant, make plain confession. To contrite hearts I do remission; Be not despaired, for I am not vengeful; ‘Gainst ghostly enemies think on My passion; Why art thou forward, since I am merciful? “My bloody wounds down railing by this tree, Look on them well, and have compassion; The crown of thorn, the spear, and nails three Pierced hand and foot of indignation, Mine heart riven for thy redemption; Let us twain in this thing be ‘greeable, Love for love, by just convention; Why art thou forward, since I am merciful? “I had, on Peter and Magdalene, pity For the great constraint of their contrition; ‘Gainst Thomas Indes’[1] incredulity, He put his [hand] deep in My side down; Roll up this matter, grave it in thy reason; Since I am kind, why art thou so unstable? My blood, best treacle for thy transgression; Why art thou forward, since I am merciful? “Think, against pride, on Mine humility; Run to school, record well this lesson; ‘Gainst false enemy, think on my charity, My blood all spilt by distillation; Why did I this? to save thee from prison; Before thine heart, hang this little table, Sweeter than balm ‘gainst all ghostly poison; Be thou not forward, since I am merciful.” “Lord, on sinners kneeling on their knee, Thy death remembering of humble affection, O Jesu, grant of Thy benignity, That the five wells plenteous of ‘fusion, Called Thy five wounds by computation, May wash in us all surfeits reprovable. Now, for Thy mother’s meek meditation, At her request, be to us merciful.”
Footnotes: [1] St. Thomas the Apostle, according to tradition, travelled to India to spread the Gospel. The ancient Christians there are thus called "St. Thomas Christians." St. Thomas also spread the Faith in Syria, and the Indian churches are heavily Syrian; perhaps the Syrians brought the patronage of St. Thomas when they went to India, or possibly St. Thomas did evangelize them himself.
Source: Frederick Furnivall, ed. Political, Religious, and Love Poems. Early English Text Society, Original Series 15. (London: Kegan Paul, Trench, Trübner & Co., Limited, 1903), 141-142.