Why does abraham lincoln use a biblical allusion in this excerpt from his "house divided" speech?

if we could first know where we are, and whither we are tending, we could then better judge what to do, and how to do it. we are now far into the fifth year, since a policy was initiated, with the avowed object, and confident promise, of putting an end to slavery agitation. under the operation of that policy, that agitation has not only, not ceased, but has constantly augmented. in my opinion, it will not cease, until a crisis shall have been reached, and passed. "a house divided against itself cannot stand."

1.) to show that he was a pious christian

2.) to explain that slavery was dividing the nation

3.) to better connect with his audience

4.)to show his commitment to ending slavery

5.) to claim that slavery violated the nation's principles