John Gill

Be merciful unto me, O Lord,.... In my distressed and miserable condition, being an object of mercy, pity, and compassion; this petition is used by Christ in Psa 41:10. for I cry unto thee daily; or "all the day"; every day, and several times in a day, Psa 55:17 constant and importunate prayer is the duty of saints, and available with God, Th1 5:17. Christ was much in the exercise of it, Luk 6:12.