But even if the soul, by perfect contrition, is freed from its guilt of mortal sin, it must according to the mind of Christ, who instituted the sacrament of Penance for the remission of sin, submit to the power of the keys committed to the priesthood and that will be the more necessary if its contrition is imperfect. While perfect contrition without the sacrament of Penance may remit sin, if the supernatural motive of sorrow is not the love of God, but a motive less worthy, _e.g._, fear of punishment, forgiveness is to be obtained only by the worthy reception of Penance. In other words, the penitent must confess his sin to a duly authorized priest, express his contrition, accept the penance enjoined by the confessor for the satisfaction of sin and be absolved by virtue of the words of Christ: "Whose sins you shall forgive they are forgiven and whose sins you shall retain, they are retained." All this is most beautifully expressed by Dante in his description of the Gate of St. Peter and its angelic keeper: "The lowest stair was marble white, so smooth And polish'd that therein my mirror'd form Distinct I saw. The next of hue more dark Than sablest grain, a rough and singed block, Cracked lengthwise and across. The third, that lay Massy above, seemed prophyry, that flam'd Red as the life-blood spouting from a vein. On this God's angel either foot sustain'd, Upon the threshold seated, which appear'd A rock of diamond. Up the trinal steps My leader cheerly drew me. 'Ask,' said he, 'With humble heart, that he unbar the bolt.' Piously at his holy feet devolv'd I cast me, praying him for pity's sake That he would open to me: but first fell Thrice on my bosom prostrate. Seven times The letter, that denotes the inward stain, He on my forehead with the blunted point Of the drawn sword inscrib'd. And 'Look,' he cried, 'When enter'd, that thou wash these scars away.' Ashes, or earth ta'en dry out of the ground, Were of one colour with the robe he wore. From underneath that vestment forth he drew Two keys of metal twain: the one was gold, Its fellow silver. With the pallid first, And next the burnish'd, he so ply'd the gate, As to content me well. 'Whenever one Faileth of these, that in the keyhole straight It turn not, to this alley then expect Access in vain.' Such were the words he spake, 'One is more precious; but the other needs Skill and sagacity, large share of each, Ere its good task to disengage the knot Be worthily perform'd. From Peter these I hold, of him instructed, that I err Rather in opening than in keeping fast, So but the suppliant at my feet implore.' Then of that hallow'd gate he thrust the door, Exclaiming, 'Enter, but this warning hear: He forth again departs who looks behind.'" (IX, 75.)