Possible meanings are 1) this is a metaphor in which the author describes the kings being afraid as if they were ships that shake because God destroys them with a strong wind. AT: "They shook with fear, as the ships of Tarshish shake when you break them with the east wind" or 2) this is an apostrophe in which the author describes God's great power. (See: [[rc://en/ta/man/translate/figs-metaphor]] and [[rc://en/ta/man/translate/figs-apostrophe]])
It is implied that what they have heard is the great things that God has done in the past. AT: "As we have heard about the great things that God has done" (See: [[rc://en/ta/man/translate/figs-explicit]])
This means that they have seen the proof that the things that they have heard are true. AT: "so we have seen God do great things now" (See: [[rc://en/ta/man/translate/figs-explicit]])