But does this commandment speak only of killing?

By forbidding murder God teaches us that He hates the root of murder, such as envy, hatred, anger, and desire of revenge, and that He regards all these as murder.

Proofs

• By forbidding murder God teaches us that He hates the root of murder, such as envy, hatred, anger, and desire of revenge, (Proverbs 14:30; Romans 1:29; Romans 12:19; Galatians 5:19–21; James 1:20; 1 John 2:9–11)
• and that He regards all these as murder. (1 John 3:15)