Digital products are purchased one time, and sold over and over again. If you buy an ebook for $5 with resale rights, you can sell that book to hundreds of customers again and again, without any further investment. 

      The Widow’s Oil

In the Biblical book of 2 Kings, we find a story of a certain widow whose husband had died leaving her in debt. She didn't have any money to pay the debt. The creditor was keenly aware of her poverty, but he was unsympathetic to her plight. His intention was to take her children and sell them into slavery to satisfy the debt. God didn't want the story to end that way. His solution was to give the widow something to sell. He put her in the oil business. She ended up being able to sell oil, get completely out of debt and live on the rest of her profits. Here's the story from Bible    

       2 Kings Chapter 4 

1Now the wife of one of the sons of the prophets cried out to Elisha, “Your servant, my husband, is dead, and you know that your servant feared the LORD. And now his creditor is coming to take my two children as his slaves!”

2“How can I help you?” asked Elisha. “Tell me, what do you have in the house?”

She answered, “Your servant has nothing in the house but a jar of oil.”

3“Go,” said Elisha, “borrow jars, even empty ones, from all your neighbors. Do not gather just a few. 

4Then go inside, shut the door behind you and your sons, and pour oil into all these jars, setting the full ones aside.”

5So she left him, and after she had shut the door behind her and her sons, they kept bringing jars to her, and she kept pouring. 

6When all the jars were full, she said to her son, “Bring me another.”

But he replied, “There are no more jars.” Then the oil stopped flowing.

7She went and told the man of God, and he said, “Go, sell the oil, and pay your debt. Then you and your sons can live on the remainder.