# Let me fall into the hand of Yahweh rather than into the hand of man

"Let me be punished by Yahweh, rather than be punished by people" 

# Let me fall

The people of Israel are the ones who would die from the plague, but David is personalizing this judgment as if he himself was being killed.

# hand of man

Here "man" is used in the generic sense of "people."

# his merciful actions are very great

"Yahweh is very merciful"