Because he knows where all the bad girls are.
St Nicholas is the patron saint of prostitutes. There was a folk tradition involving shoes left on the hearth overnight-- Père Noël brings gifts for the good children [and prostitutes]. I can't find a text version but here are two illustrations. In the first, Père Noël has left a young satyr. In the second, a bearded putti offers a selection of wealthy clients.
|Étrange Noël (Strange Christmas) by Henry Gerbault 1917 Le Sourire.|
|Prostitutes discovering their Christmas Gifts, French School, 1893|
Icons and paintings often show St Nicholas with three bags or balls, symbolising the three bags of gold he tossed through the chimney of the home of the poor man for the daughters' dowry, so they would not be sold as prostitutes. Thus he is seen as the "gift-giver." (CATHOLIC.ORG)
|Saint Nicholas with 3 golden balls.|
St Nicholas' story was recorded and embellished by Symeon the Metaphrast[a hagiographer, the Compiler, 10th c collector of saint legends, one time a byword for absurd fabrications. ] Symeon's narrative shows its origin in the oral tradition. I can imagine the storyteller acting the part of the father, assaying the bag of gold.
There was a man, once famous, who had fallen into obscurity and from riches to poverty. He had been reduced to extreme want in all material ways. When the day came that he lacked the very essentials of life (ah, shame! to what extreme does poverty progress!), he determined to sell into prostitution at a price his three beautiful daughters to whoever were willing to buy, with the profit from each to sustain himself and them. It was impossible for him to marry them off; for because of their excessive poverty, all beaux disdained them. Now once having convinced himself, he pondered the disreputable plan, and was already making the first move toward that shameless act. But Thou, Lord, Who art by nature both good and the source of every good, and dost benignly hearken to our needs, didst convey news of this plight to the ears of Nicholas. And Thou didst send him like a good angel and ready helper to that poor man, who had already reached the point of decision, that Nicholas might at one and the same time relieve his poverty and free him from that which was more oppressive than poverty....blah blah moralizing about charity...
So, after Nicholas had bagged a sum of gold, in the dead of night he went to that man's home. The minute he had thrown the bag through the window, he hastily returned to his home, disquieted at the thought of being seen. When the poor man arose later in the morning, he found the gold. Loosing the string with difficulty, he was dumfounded, thinking himself deluded and fearing that what he saw before him was fool's gold. For in such circumstances how could he imagine that a benefactor would be willing for him to benefit without knowing the source of the benefaction? Then assaying the gold with the sensitive tips of his fingers and scrupulously testing it, he concluded that it was in fact gold. He was elated, he marveled, he was transported. In the realization of such joy he shed warm tears. Mentally checking down the roll of all his many acquaintances, he could find none to whom he could ascribe what had been done. He attributed this gift to God, incessantly and tearfully rendering thanks to Him. Then with overflowing heart he strove before all else to erase the mischief of his sin against God.
He married off one of his daughters, the eldest of course, providing as dowry for her the mysterious gold which had so abundantly been supplied.
Yet at a later time it came to the attention of the remarkable Nicholas and he verified the fact, that the man was preparing to carry through a resolve to sell the second of his daughters, despite his vain hope that through marriage he might avert a second such evil occasion. Thereupon, unperceived by anyone, during the night Nicholas threw an equally valuable bag of gold through the same window.
|Masaccio - St. Nicholas Saving Three Sisters from Prostitution|
And so again, when the man arose in the morning and found the gold as before he was once more dumbfounded. Prostrate on the ground he wet the earth with his hot tears, saying: "God, Who dost gladden the wretched and are the font of our well-being, Who even once didst become man for my disobedience, and now hast freed me and my daughters from the snare of, the Enemy, show Thou me the one who obeyest Thy will, who is angel among men and reflector of Thy goodness. Who is this man who has snatched us from the poverty which overwhelms us, and freed us from our loathsome intentions? For lo, out of Thy mercy I now give a daughter to wed, conjoined in lawful matrimony. Till now she has escaped becoming the prey of the Devil and a source of profit for me. What a sorrow, that—more overwhelming than any other catastrophe to me!" He uttered this prayer, and forthwith arranged for the marriage of his second daughter
He was now consumed by a firm belief and high hope that the same evil occasion would not arise with respect to the third daughter. Surely a bridegroom could not be lacking! Because of the previous happenings he confidently imagined that in the instance of this daughter he would have her dowry ready at hand. As a peer of her sisters she should receive equal generosity. This time he waited, watchfully, night after night on guard, to anticipate that singular disburser of money when he came again unannounced. If and when he should come again, he would learn from that person who he was and why he was distributing gold in this way. The father watched very carefully, awaiting the unknown's appearance.
Then at the third hour in the dead of night, the servant of God Nicholas came to the now customary spot with silent tread, and now again threw a tied bag of gold through the same window, swiftly retreating toward home The girls' father, when he heard the sound of gold as it struck and realized that it was the anticipated gift of wealth, as fast as he could ran after the man. When he caught up with him and recognized who it was (for because of his family's position and celebrity Nicholas could not hide his identity) he dropped to Nicholas's feet, calling him redeemer, reviver, savior of souls who were foundering in dire peril. "For had not," he said, "the good Lord in His compassion awakened thy pity, then long ere this, alas unhappy me!, I would have perished with my three daughters. But now through you God has granted salvation to us and freed us from the mischievous mischance of sin. He has lifted the indigent from the mire and caused the poor to rise from the poverty also."
These words he uttered with tears of joy and in the warm glow of faith. Then Nicholas, as soon as he realized that he had failed to keep his identity hidden from the man, made him arise. He bound the man by an oath never in the whole course of his life to relate to others what had occurred, or to make known the benevolent act. Now all the actions of the marvelous Nicholas, this one is the most charitable and the best known.