It's a line from the Christmas favorite, Silent Night. Jesus's arrival, they say, was "the dawn of redeeming grace".
Think about it. For millennia God-fearers -- from Abel and Noah and Job on up through the Jews and converts -- had been sacrificing and going through the rituals God put into place that provided salvation. These all pointed to One person -- the Incarnate Son of God. So on that day when the Christ arrived, we see the culmination of God's plan to save His creatures out of His own amazing grace and mercy.
It's the most wonderful time of the year, not because of tinsel and songs and decorations and snow or even gifts. It is the most wonderful time of the year because it points to that highest Gift, that stunning moment when the God of the Universe became flesh and dwelt among us, bringing with Him a grace previously unknown -- redeeming grace.
Praise God from whom all blessings flow.