How was the Bible used to reduce modern slavery? In debates over slavery in the United States, many abolitionists used the Bible as part of their reasoning for freeing the slaves.  

In both the Old &amp; New Testaments there is very clear statements that holy people had slaves.

Genesis 17:13


  He that is born in thy house, and he that is bought with thy money, must needs be circumcised: and my covenant shall be in your flesh for an everlasting covenant.


II Kings 4:1


  Now there cried a certain woman of the wives of the sons of the prophets unto Elisha, saying, Thy servant my husband is dead; and thou knowest that thy servant did fear the Lord: and the creditor is come to take unto him my two sons to be bondmen.


Colossians 4:1


  Masters, give unto your servants that which is just and equal; knowing that ye also have a Master in heaven.


Matthew 18:25


  But forasmuch as he had not to pay, his lord commanded him to be sold, and his wife, and children, and all that he had, and payment to be made.


How did abolitionists reconcile these two beliefs?
I think this could easily become an answer about American history and and politics unless we confine our answer to usage of the Bible. Flimsy is right in his comment above - the Bible does not condone slavery, but it does not officially abolish the institution (much like the US Constitution). What it does do is place Christ in the master-slave relationship, giving even slavery the possibility of redemption.

Colossians 4:1 (KJV)
1 &quot;Masters, give unto your servants that which is just and equal; knowing that ye also have a Master in heaven.&quot;
Colossians 3:22 (KJV)
22 &quot;Servants, obey in all things your masters according to the flesh; not with eyeservice, as menpleasers; but in singleness of heart, fearing God:&quot;

These verses do not answer for using the Bible to abolish slavery, but they could justify a move to abolish it, since it has &quot;become destructive of these [Christ-Centered] ends&quot; and so it is their duty &quot;to alter or abolish it.&quot; At least in the United States. In first-century Roman society, it wasn't written in the social framework to be able to reform slavery, or any institution for that matter. But Christians everywhere in all societies do what they can to proclaim Christ until He comes, as many abolitionists did in their efforts.