In chapter 20 of Candide, can you explain what does Martin think about God and why?

Martin the scholar believes that God has cruelly abandoned the world. He thinks this because, wherever you look, men are always at each other's throats and killing each other. This unshakable conviction is confirmed by the events that he and Candide witness on the high seas. En route to Bordeaux, the two men watch a particularly intense sea battle. One of the ships sinks, and the entire crew perishes. By recognizing one of his stolen jewel sheep floating in the water, Candide is able to identify the ship as belonging to the cruel slave-owner Vanderdendur.
Candide claims that Vanderdendur's death shows that there's some justice in the world after all; this wicked man got what was coming to him. But Martin disagrees. It wasn't just Vanderdendur who went down with the ship but his crew as well. This is why Martin thinks that God has effectively abandoned his creation. The innocent are punished alongside the guilty, the good with the evil.