Gibbs, Jeffrey A. “Matthew 5:21-26: On Murder.” St. Louis: Concordia Publishing House, 2006, pp. 280-285.
Commenting on Matthew 5:21, Gibbs makes it clear that Jesus was not necessarily saying anything radically new. “The belief that anger deserves punishment just as much as actual murder does was found elsewhere in early Judaism” (Gibbs 2006, 280). Rather, Jesus is making observations about what his hearers might have heard and contrasting that with his correct interpretation. Others had also reached those conclusions.
The interpretation must also be tempered. For instance, Gibbs notes that while Jesus says not to call someone a fool, he himself uses the term of the Scribes and Pharisees (Gibbs 2006, 282). He seems rather to speak of a careless or angry and unthinking use of the idea.
Reconciliation is certainly a high priority. It does not replace an offering, but it can interrupt the process. It is important enough that failure to do so could rightly result in imprisonment (Gibbs 2006, 283).
The essence of the passage is clear. “The believer cannot pretend that the horizontal relationships that he carries on with his fellows are independent of his relationship with God. His vertical relationship with God must affect his horizontal relationships with his brothers” (Gibbs 2006, 284). Gibbs takes this to apply also to the approach to the communion altar.