In the Old Testament, God’s stretched out hand is a sign of condemnation. That is clearly not the meaning of this stretched forth hand. The hand would have been an invitation, a welcome.
The people might have wondered if the being who came to them were an angel, but Jesus makes certain that they know who he is. Not only does he give his name (Jesus) and title (Christ), but he makes sure that they understand that he is the very one whom the prophets “testified shall come into the world.”
Now understanding that they were in the physical presence of their God, they fall to the earth. That action is often noted in the Book of Mormon as a representation of being overcome by the Spirit. If the spirit could have that effect, how much more of an effect would the very miraculous and dramatic appearance of the being they have known as God make.