The second command helps to explain the first one. The first command says that God’s people must worship him alone. The second command says how they must worship him. They must not make an idol.
An idol is an image. People could make these images out of wood or stone or gold. The image could represent one of the false gods. Or an idol could represent the true God. In either case, God did not want his people to make an idol for themselves to use in worship.
There is only one God. There is only one true faith.* But the nations near God’s people had many false gods. The people of God would see these false gods and be tempted to follow them. Or they could be tempted* in another way. They could decide to worship the true God in the same way that the other nations worshipped false gods. The second command says no to both of those things.
God made the heavens and everything in them. He cannot be represented by something that looks like one of the things he has made. He made the heavens and the earth, the seas and the things under the sea. He is greater than all he has made. No idol can ever show all that is true about him.
Many years after Moses,* God sent prophets* to speak for him to the people. The prophets warned the people to stay away from idols. They told the people that God wanted to be their God. He wanted them to be his people. He wanted to be as close to them as a husband is close to his wife. So, they must be loyal to him. When a wife searches for another man to give herself to him, she is not loyal to her husband. What she does brings shame to their house. In the same way, when Israel* chose to follow a false god and worship an idol, the nation was not loyal to God. This would bring shame to the nation. They would bring shame to God’s name. The prophets warned them never to do this. They were God’s own people. They were to be loyal to God and obey him completely.
When people follow a false god, they have no god at all. An idol is only the work of human hands. ‘They have mouths, but they cannot speak. They have eyes, but they cannot see. They have ears, but they cannot hear. They have noses, but they cannot smell. They have hands, but they cannot feel. They have feet, but they cannot walk. They cannot make sounds come out of their mouths.’ 
Yes, sometimes an idol may appear to have power. Honoring* an idol can sometimes seem to make a good thing happen. But this power does not come from a god. This power comes from Satan,* the Evil One* or the spirits* who follow him. Moses even says that when a person makes a sacrifice* to a false god, they bring a gift to an evil spirit
Evil spirits can make an idol seem as if it can do something for you. They can act like gods. They can even do wonders to fool the people who follow a false god. Evil spirits hate the true God. They always lead people away from God. If a person follows an idol it will always lead far away from God. That will always lead to trouble.
After God gives this command, he says. ‘I, the Lord* your God, am a jealous God.’  Sometimes, the word jealous can describe someone who acts in an evil or selfish way. But God is neither evil or selfish. So, what does he mean?
First, God is not jealous of other gods. God is jealous for his own name, his own honor. If the people followed another god, the true God would lose the honor that belongs to him.
But he is also jealous in another way. God is jealous for his people. He wants what was best for them. He knows that if they follow any other god, they will suffer. They would become slaves again to these false gods. Soon, they would become the slaves of other nations as well. They would no longer have God’s blessing.* Instead, they would face God’s anger. That is why God spoke in such a strong way. He did not want them to forget.
God gave the command because he loved them. He gave these laws* to protect them. As long as they followed the commands, he would be their God. And they would be his people.