Imagine that your ankle is tied to a post by a long chain. your master, who owns you, tied you to the post. you can move enough to do the work he wants you to do, but there is no way to get free, and you can’t move beyond the circle where that chain moves. Moreover, the work the master wants you to do is not even good work, it is making a product that hurts other people. You have no way to get any food or drink except what the master feeds you, and it is not even very good nutritious tasty food, but you get so hungry you eat it anyhow.
That is slavery, now how did you get to be a slave? The master had something you wanted very much, you knew it was not good for you, but it was very attractive, pretty, exciting, pleasurable and made you feel good inside, good about yourself, and was a lot of fun. He told you this thing would make you happy all your life, and would make you better than anyone else. All you had to do to enjoy this gorgeous thing was to do a little job for him. So you went to work for him, and before you knew it, bam, the chain was on, and you were his prisoner, bound to work for him.
Now imagine someone has come along, paid the price for your freedom–giving away all that he owned to do so–and has cut not only your chains, but the chains of all the other slaves, and you are now free. You gladly follow him, and do anything you can to show your gratitude. he also shows you things that are so much better, more attractive and more desireable than the false glamour that attracted you to your old master. All you have to do is help him in his work of freeing other slaves, which you gladly do.
But some of the slaves, even when their chains are cut, stay where they are, and continue to do the work of their old master and eat his food. They could get up an leave anytime, but either they don’t believe the stranger has power to cut the chains, or they are afraid of the new life, or they have a warped attachment to the old slave master. They are slaves still, even though they are free to leave any time, they are slaves by their own foolish choice.