Arguments used by slaveholders before and during the ACW regarding Biblical slavery:
There are numerous passages dealing with the institution in the Old Testament that the slaveholder used in justification: Genesis xx. 14, xxiv. 35, Leviticus, xxv. 45, so on and so on.
God sanctioned Abraham as a slaveholder (Gen. xxiv. 35, xxvi. 12).
The 4th Commandment (exod. Xx. 10) provides rules for masters and slaves on the Sabbath.
Further, Exodus xxi. 2 to 6 provides sanction, it also touches on the year of Jubilee whereby slaves could be freed. However, such Jubilee was reserved only for Hebrew slaves, not gentiles (See Leviticus xxv. 44 to 46). (Slavery was dealt with differently when it came down to Hebrews and gentiles, yet the institution of slavery as "involuntary servitude" was recognized and sanctioned by God. In fact, gentile slaves were heritable property.)
In Numbers, it is clearly stated that the spoils of war included human beings, slaves for life (gentiles), according to the law of Leviticus, ch. xxv. All spoils of war were to be included in the tribute to God (a commandment of God). In verses 40 and 46, we see the tribute of slaves to God along with donkeys, cattle, sheep, etc. These slaves (gentiles) became the property of the ministers of religion. The supposed exception in Deuteronomy xxiii. 15, 16, only applies, again, to Hebrew slaves, not gentiles. If God demanded tribute of slaves unto Him, Slaveholders would argue, then how can the institution of slavery be morally wrong? It was viewed as a permanent institution; duties between master and slave were defined; the rights of masters protected. And though the Bible does not demand that countries or people own slaves, it is no sin for those to own them.
New Testament – Slavery different from divorce and polygamy. The two latter were expressly condemned in the New Testament (See for example Mathew xix. 3 to 9.) Conversely, domestic slavery is not forbidden in the New Testament, but is permitted, authorized and regulated. The absence of any condemnation of slaveholding in the New Testament was proof to the slaveholders that it was not unlawful.Christ and his apostles preached in the midst of slaves and slaveholders. In the New Testament the apostles give formal enumerations of previous sins of their time. (See Romans i. 29, 31; Galations v. 19-21; Mathew xv. 19; Colossians iii. 8, 9; 2 Timothy iii. 2-4.) The owning of slaves never appears among these sins. To southerners (slaveholders), if it was deemed morally wrong during Jesus' time, why did he not condemn it? In fact, Christ applauds a slaveholder in the New Testament. (See Matthew viii. 5 to 13, and Luke vii. 2-10.)The New Testament teaches that the conditions of a slave, although not desirable for its own sake, has no essential bearing on the Christian life. They cited) 1 Cor. xii. 13, "For by one spirit we are baptized into one body, whether we be Jews or Gentiles, whether we be bond or free: and have all been made to drink into one Spirit." Further, in Galat. iii. 28, "There is neither Jew nor Greek; there is neither bond nor free; there is neither male or female; for we are all one in Jesus Christ." Southerners used this to dispute the claim that they could not love their neighbor as one's self even if that meant between master and slave.
As to "Chattel" slavery, southern slaveholders would have insisted that such a definition was incorrect, asserting, probably, that such a definition implies property in the very personality and soul of the slave as well as the labor. Slaveholder's (naturally) would have argued that only property over the slave's labor was at issue, not his soul or personality. They would point to laws in existence which would prove that only labor for life without the slave's consent for the master was at issue. In other words, or in theory, the slave retained personhood, was not a mere thing or commodity.
All that sounds crazy to us moderns, but that was the line of argument used. Was also part-and-parcel to 1 million casualties between 1861-65.