This famous parable offers "heavenly rewards" to those of a kind and generous nature but the parable makes it clear that the compassion of the "elect" was not expressed as an act of conscious devotion to God who resides in those whom they helped. Is it enough, spiritually speaking, to be a humanitarian, perhaps an agnostic, even an atheist? Yes--but only up to a point.
We can get good karma and the heavenly rewards of heart warming satisfaction from our good deeds. But to reunite our souls with God, our Creator, requires an act of conscious devotion (and not just one!) All of our good karma for our generosity might be used up by our response when we are attacked by others for it is an axiom that "no good deed goes unpunished" in this world of duality! Good karma can work off bad karma but until we begin to yearn to step out of duality all together and into transcendence (the oneness of God's eternal love and bliss), we just remain on the merry-go-round.
Thus a loving parent may have to discipline a child (but to do so does not require being angry); a policeman may have to apprehend a criminal (but need not be cruel); a teacher, correct a student (without dislike); and a supervisor, to lay off or let go an employee (without malice). True love IS wisdom. We mustn't forget that.
But I think there's another reason, as well. For the fellow feeling of kindness and warmth which we call the Christmas spirit is reflected in the innocence, natural love, and openness that children express. (This is also depicted in the "softly lowing" animals who share the humble stable where Jesus is said to be born.)
Paramhansa Yogananda often quoted these words of Jesus, "Suffer the little children to come unto me, for of such is the kingdom of heaven."
Giving to those in need affirms our kinship even with those whose circumstances differ so greatly from our own, or whose outer appearances do not attract us. We are all children of God and are equally deserving of the divine abundance of joy and self-respect.
Whatever may be the roots of our present troubles, or those of others less fortunate seeming than us, each of us can turn the "sow's ear" of difficulties into a "silk purse" of spiritual growth if we respond with grace, faith, equanimity, and cheerfulness. Our tests exist to cleanse us and awaken our strength, courage and faith.