John Calvin Commentary Genesis 12:5

"And Abram took Sarai his wife, and Lot his brother`s son, and all their substance that they had gathered, and the souls that they had gotten in Haran; and they went forth to go into the land of Canaan; and into the land of Canaan they came." — Genesis 12:5 (ASV)

The souls that they had gotten in Haran. Souls signify male and female servants. This is the first mention of servitude, from which it appears that not long after the deluge, the wickedness of man caused liberty, which by nature was common to all, to perish for a great part of mankind.

How servitude originated is not easy to determine, unless, according to the commonly prevailing opinion, it arose from wars, because the conquerors compelled those whom they took in battle to serve them, and from this the name “slave” is derived. But whether those who were first slaves had been subjugated by the laws of war or had been reduced to this state by want, it is indeed certain that the order of nature was violently infringed, because men were created for the purpose of cultivating mutual society with one another.

And although it is advantageous that some should preside over others, yet an equality, as among brothers, should have been retained. However, although slavery is contrary to that right government which is most desirable, and in its beginning was not without fault, it does not, on this account, follow that its use—which was afterwards accepted by custom and excused by necessity—is unlawful.

Abram, therefore, might possess both servants bought with money and slaves born in his house. For that common saying, “What has not prevailed from the beginning cannot be made valid by the passage of time,” admits (as is well known) of some exceptions; and we will have a relevant example in Genesis 48:1.