During Biblical times there was a type of slavery known as a bond-servant. Such a "slave" would be in a contractual arrangement with the master and would be paid. However, in order to leave the arrangement, certain conditions needed to be met. The main condition was usually payment of an amount of money. However, this form of slavery needed to be voluntary, you could not for instance kidnap someone and force them to be a slave. To do so, according to the Bible, is a terrible crime. If you force someone to be a slave and keep them in your possession or sell them to someone else you are guilty of a capital offense. The Bible is even tougher on slavery than we are in society today: "He who kidnaps a man, whether he sells him or he is found in his possession, shall surely be put to death." (Exodus 21:16)
A positive perspective on everything.