If you want more information on arcing, see here.
Here's my arc, and a short reflection:
Main point: We ought to be reconciled to our brother, even if that means leaving our gift before the altar.
Arcing commentary -
v.23 and 24 give us a very clear "If-Then" so they are the major arcs of the two verses - If you are offering and remember your brother has something against you, then leave your gift and be reconciled.
v.23 has two main points: You are offering and remember your brother has something against you. These two ideas could be joined with "S" - Series, but series typically should be reserved for when you state multiple events with no dependence.
In this sentence, there is a progression: First you're offering, and there "you remember your brother has something against you." That means the second idea depends on the first already happening, so I use P.
There is locative relationship in v.23 "before the altar." It serves to highlight that it's there before the altar that this happens. Even right before you're about to offer a sacrifice to God you ought to be reconciled.
v.24 has two main ideas, so they go under major arcs - "Leave gift and go; first be reconciled then come and offer." Both contain progression relationships - First one, then the other.
The tricky piece, "how are these two arcs in v.24 related?" The arcs essentially restate one another, saying the same thing in two different ways, but the second one gives a more detailed account and further explains the first. That means we have either "Id-Exp" or "Ac-Mn." Id-Exp would mean that the second sentence explains one of the ideas (nouns) listed in the first. Ac-Mn means that the second sentence explains one of the actions (verbs) of the first. Since we Jesus is explaining more about what "leave and go" mean, we ought to use Ac-Mn.
Passage commentary -
Jesus has just said that not only is the brother who murders liable to judgment, the brother who is angry with another is liable to judgment (v.21-22). Then he proceeds to give one application of what this means - we ought to be reconciled to one another. Jesus does this by giving the most extreme example.
Even when we are just about to offer a gift before God and remember our brother has something against us, we should leave our gift there and be reconciled first. While at first this seems like it doesn't follow from what was said before (what's known in logic as a non-sequitur), it actually does because Jesus is highlighting how serious anger is. Anger and it's consequences are so serious we ought to go out of our way to keep someone from sinning in that way.
Jesus does not allow the possibility that we can stand innocently by while others get angry at us, we must go and be reconciled. It is insufficient to say, "well, at least I am not angry at anyone," we ought to think and ask, "is anyone angry at me?"
So, Christian - Go and be reconciled. Do it now and today, lest you find yourself about to offer a gift to the Lord and there remember and have to do it then.