But Melchisedech the king of Salem, bringing forth bread and wine, for he was the priest of the most high God. (Gen 14:18)
The Lord hath sworn, and he will not repent: Thou art a priest for ever according to the order of Melchisedech. (109:4)
Prayer for Priests by the late John J Cardinal Carberry:
Keep them; I pray Thee, dearest Lord.
Keep them, for they are Thine
The priests whose lives burn out before
Thy consecrated shrine.
Keep them, for they are in the world,
Though from the world apart.
When earthly pleasures tempt, allure —
Shelter them in Thy heart.
Keep them and comfort them in hours
Of loneliness and pain,
When all their life of sacrifice
For souls seems but in vain.
Keep them and remember, Lord,
they have no one but Thee.
Yet, they have only human hearts,
With human frailty.
Keep them as spotless as the Host,
That daily they caress;
Their every thought and word and deed,
Deign, dearest Lord, to bless. (Found Here)