How do we know that anger can be sinful?

In Matthew 5:22, Jesus says that anyone who is angry with their brother without cause will be in danger of judgment. This teaching reveals that sin is not merely about outward actions but also about internal attitudes. When anger leads to derogatory words like 'Rakar' or 'fool,' it signals a deeper heart issue that reflects a desire to harm others. This teaching challenges believers to examine their hearts and motives, recognizing that sinful anger is just as serious as the act of murder itself.