What does Psalm 118:3 mean?

The repeated phrases in this psalm suggest the "call and response" model where a congregation replies with specific words in response to a prompt. God is proclaimed here using a Hebrew term for loyal, consistent love found elsewhere to describe God (Exodus 34:6). Israel was tested and disciplined (Jeremiah 25:8–9), but the nation survived (Ezra 2:1; Jeremiah 29:11) because of the Lord's steadfast love for them.

This response evokes Aaron and his family line. Aaron was Moses' brother (Exodus 7:2). Aaron's descendants were the family line of Israel's priests (Exodus 30:30). These had ample reason to thank the Lord for His provision. Even though the temple had been destroyed (2 Kings 25:1, 2 Chronicles 36:17–21), God had not allowed His chosen people, or their faith, to disappear.