The first sentence in Isaiah 1:18 about reasoning together seems so out of place compared to what's around it - at least to me. Can you help me understand the context a little bit better? Also if you know of any other passages that show God encourages us to use reason and test the things we hear to understand the truth I'd certainly appreciate it.
""Wash yourselves, make yourselves clean; put away the evil of your doings from before My eyes. Cease to do evil, learn to do good; seek justice, rebuke the oppressor; defend the fatherless, plead for the widow. Come now, and let us reason together," says the LORD, "Though your sins are like scarlet, they shall be as white as snow; though they are red like crimson, they shall be as wool. If you are willing and obedient, you shall eat the good of the land; but if you refuse and rebel, you shall be devoured by the sword"; For the mouth of the LORD has spoken" (Isaiah 1:16-20).
Isaiah is addressing the reluctance of people to change. People often get trapped in the mindset that they are too sinful to be forgiven. God is saying that line of thinking is not reasonable. God is able to forgive the worse of sinners if they leave their sins. A similar passage is found later in Isaiah 55:6-9. Just because a man doesn't see how it is possible, it doesn't make it impossible with God.
The number of passages inviting people to reason with God is huge. Read through Ezekiel 18:21-32 and you will see God arguing from logic how He forgives the sinner. In fact, I wrote a small book on the subject. See Keys to Understanding.