The 19th century Spanish philosopher, George Santayana, famously wrote, ″Those who forget the past are condemned to repeat it″. In other words, we should learn from our mistakes. We can't change what we've done, but wise people can ensure that they'll do things differently in the future.

Psalm 78 has two purposes. First, it is a ″parable″ (v. 2), a story that is intended to teach us how to live wisely. Like the writers of Proverbs, the psalmist is a man who is passing on ″things we have heard and known″ (v. 3)–namely, lessons from Israel's history–to future generations.

The poet begins by reminding his readers that God had given the law to enable them to trust and stay faithful to Him (vv. 5-8). However, Israel had a history of repeatedly sinning against God and putting Him to the test. They kept forgetting what God had done for them, ″the wonders he had shown them″ (v. 11): God's saving power in sending plagues on Egypt, dividing the Red Sea, providing bread and food in the wilderness, and giving them the promised land (vv. 12-16; 23-29; 42-55). Their failure to remember God's goodness led to a failure to live in the right way again and again. Yet, even though He punished them for their sin (vv. 59-64), God didn't give up on them because He knew they were weak (v. 39).

The second purpose in Psalm 78 is to show that God will not allow this cycle of sin, judgment, and forgiveness to continue. He has acted decisively to change the future. He has chosen to live amongst His people in His sanctuary (vv. 68-69) and, more importantly, chosen David to shepherd His people ″with integrity of heart″ (v. 72).

This psalm, like so many others, drives us to Jesus. Even God's chosen shepherd, David, failed and compromised his integrity. But our one true king, Jesus, is the good Shepherd who leads and protects us perfectly.

Hebrews 2:3 warns Christians, ″how shall we escape if we ignore so great a salvation″. We must pass on to the next generation the parable of the wonders of our salvation, which is all that Jesus has done for us to bring us to God and give us eternal life. Preachers and teachers in the church need to remind our people about the parable of their salvation regularly, so they will remember what Jesus has done for them and live in the right way.