In context, God supplies this invitation to Israel while they are in rebellion against Him. Though they are committing every kind of wrong imaginable, He invites them to sit down and reason together with Him. Jesus says that He did did not come to call the righteous, but sinners, so there is a great deal of consistency in the invitations.
I felt compelled to look up the verb tenses and moods and such, because I am that kind of word nerd, and found a couple of things to be very interesting.
First, the invitation to come is in the imperative. This is not so much a request as a command. It is comparable to a parent with a rebellious child saying that they need to talk. It is not an invitation so much as a command to park it and get to chatting. There are those who would chafe at God striking such a tone, but He frames His relationship with such as are His in the context of Father and child. So the tone is appropriate. Moreover, the verse is not addressed to the pagans and non-Israelites, it is addressed to the Israelites; God’s chosen people.
Second, the invitation to reason together is in the imperfect which means that it can be understood as an ongoing action. God is not saying that He expects Israel to have a sit down with Him one time and then everything will be copacetic thenceforward. What He is saying is that He expects this to be an ongoing conversation; a running dialog between Him and those He has chosen. In short, He is inviting them to a relationship, not a religion.
Great. This verse is handed down to Israel. What is that to me? Rather a lot, actually. Malachi will later record God’s statement that He does not change. If God does not change, then His offer to Israel is open to all who choose to follow Him. He commands them to sit and invites them to talk. He does the same for the Christian. Jesus told His disciples to get to a secret place and talk with the Father. Jesus commands the believer to do what God here commands Israel to do: Sit down and reason with God.
Why sit and chat with God? What good does it do? Quite a bit. God makes a promise in this verse. He promises that my sins, though they be like scarlet and red as crimson, will be white as snow and like the whitest wool. His promise is cleansing. More promises follow in the verses after this — promises of blessing to the obedient and discipline to the disobedient — and those promises, in their generalized phrasing, still hold true to the Christian.
Let me sit and reason together with God this and every morning. As I do so, I will gain a relationship with Him, understanding of His Word, and other blessings to be named by God at a later date.