Psalms 89:28

My mercy will I keep for him for evermore, and my covenant shall stand fast with him.

The promise belongs to a recounting of the rich blessings bestowed upon God's people. That recounting sets those abundant benefits in contrast with the poor return made for them. Its place is therefore among reminders of divine goodness met with human ingratitude.

The mercy spoken of is to be kept for David forevermore. The covenant with him is to stand fast without failing. Those assurances extend beyond David himself to his house. They look forward toward the eternal ages and find their complete fulfillment in Christ.