958 B
Jesus continues to teach his disciples. This event began in Matthew 5:1. Jesus is talking to a group of people about what might happen to them as individuals. "You have heard" and "I say to you" are spoken to the group using plurals. "You will not kill" is singular, but you may need to translate it as plural.
But I say
The "I" is emphatic. This indicates that what Jesus says is equally important to the original commands from God. Try to translate this phrase in a way that shows that emphasis.
kill ... kills
This word refers to murder, not to all forms of killing.
brother
This refers to a fellow believer, not to a literal brother or a neighbor.
worthless person ... fool
These are insults for people who cannot think correctly. "Worthless person" is close to "brainless," where "fool" adds the idea of disobedience to God.
council
This was likely a local council, not the main Sanhedrin in Jerusalem.