Having seen the child themselves, they had now evidence that would satisfy others; and accordingly they became the first preachers of the "gospel," and went and proclaimed to others that the Messiah had come.
One of the first duties of those who are newly converted to God, and a duty in which they delight, is to proclaim to others what they have seen and felt. It should be done in a proper way and at the proper time; but nothing can or should prevent a Christian recently converted from telling his feelings and views to others - to his friends, to his parents, to his brothers, and to his old companions. And it may be remarked that often more good may be done then than during any other period of their life.
Entreaties then make an impression; nor can a sinner well resist the appeals made to him by one who was just now with him in the way to ruin, but who now treads the way to heaven.
[From Barnes' Notes on the Bible]