Question

"The obligation of human beings to

support and obey human governments,

while they legislate upon the principles

of the moral law, is as unalterable as

the moral law itself."

In your words, what is Finney saying?

Answer 1

What Finney is saying is that, if legislation is made by the government based on underlying moral principles (he refers to this moral principles as moral law), then, said legislation is as valid as the moral principles than inspired them.

For this reason, citizens are obliged to respect the legislation, because this act is equivalent to acting under one's own moral principles.