Let me tell you a little about the situation God's people were in when he spoke to them the words at the top of this page. God's people, the Israelites, were living among people who worshipped a whole crowd of so-called gods. There were gods of the hills and gods of the valleys, gods of the rivers, gods of thunder, lightning, the sun and the stars. The people who worshipped these false gods made idols representing them and they bowed down to these idols.
God did not want his people to be tempted to join in the worship of these gods - they could not do anything to help them as they were not real, and some of their worship was cruel and horrible. God hated the thought that his people would be caught up in such evil things. He was jealous for them, just as a loving husband would be if he saw his wife going off with another man. God loved them, he cared for them and he didn't want them to be hurt by going the wrong way.