Moses in his farewell addresses warned Israel not to chase after other gods and remain loyal to the Lord and his covenant. If they refused to heed his warning then God would punish them. Israel failed to listen and attempted to have a pluralistic society; worshiping the one true God along with fictional gods. As Moses predicted God punished Israel and they went into captivity. In 539 B.C. the Babylonians destroy Jerusalem and the temple. The Jewish people learned that God was serious about what he said.
What Moses said was true then, and it is true today. And we, like Israel, really don’t think God is serious about what he says. We pretend that God does not see or hear us, and therefore, our particular sin doesn’t count. The Jewish people had to learn the hard way; God was serious. Maybe it is time we got serious about God before he gets serious with us.