By John Blake, CNN

(CNN) - How did churchgoing, Bible-worshiping Christians justify holding slaves? It’s a question I’ve long had as a Civil War buff and that has new resonance on Tuesday, which marks the 150th anniversary of the start of the Civil War.

I’ve read books about politics and generals during the war. But I hadn't read much about the religious dimension to the Civil War until I came across a recent USA Today column.

Henry G. Brinton, a pastor at Fairfax Presbyterian Church in Virginia, writes that the Bible was used a weapon by both the North and the South. Brinton says some contemporary Americans are making the same mistake their Civil War ancestors did by twisting the Bible to support their own battle cries.

Brinton, author of “Balancing Acts: Obligation, Liberation and Contemporary Christian Conflicts,” says both the Union and the Confederacy invoked the Bible to justify their positions on slavery.

Slaveholders justified the practice by citing the Bible, Brinton says.

They asked who could question the Word of God when it said, "slaves, obey your earthly masters with fear and trembling" (Ephesians 6:5), or "tell slaves to be submissive to their masters and to give satisfaction in every respect" (Titus 2:9).

Christian opponents of slavery elevated biblical principles of justice and equality above individual passages that approved exclusion, Brinton says.

He wonders if a new biblical approach is needed today, as people grapple with polarizing issues like gay marriage.

Opponents of gay marriage, ﻿Brinton notes, follow a literal approach to the Bible when they cite Old Testament passages that declare, "You shall not lie with a male as with a woman; it is an abomination" (Leviticus 18:22).

He wonders if ﻿gay marriage foes are making the same mistake as defenders of slavery:

But perhaps reproduction is no longer the goal of every person and every marriage. Many couples choose not to have children, or marry late in life when they are unable to produce children. The New Testament values of faithfulness, love, sacrifice and promise-based commitment can be practiced by heterosexual couples without children — and by same-sex couples as well. Discussions of gay marriage can focus as much on scriptural equality as on the ability to reproduce.

At the same time, Brinton says liberal Christians may be making their own mistakes with their approach to the Bible:

Liberals also use Scripture for their purposes, citing commandments such as "thou shalt not kill" (Exodus 20:13) whenever a war breaks out or the death penalty is being debated. But the commandment is actually a prohibition against murder, arising out of blood feuds and vengeance killings between ancient clans and families. A literal reading of this verse does not give us the moral and political guidance we need today.

Brinton says Abraham Lincoln offered the most constructive religious perspective during the Civil War. "My concern is not whether God is on our side," he said. "My greatest concern is to be on God's side."

What do you think? Is it fair to invoke the Bible for political causes?