On one level, it is totally unnecessary to call on God to remain faithful. He is faithful to all of his promises. There is no chance that God will forsake his people.
However, our circumstances do not always seem to conform to this truth. We see evil in the world and trouble in our own lives and we wonder, Is God truly with us?
The writer of this psalm had had confidence in God from his youth (see Ps 71:5–6), but now that he had grown old he was worried because his enemies had sensed his weakness and had closed in on him. Their assessment was that God had forsaken him in his old age.
From this perspective—pouring out his honest emotions—the psalmist called on God to protect him. He asked God to remember his promise not to forsake him. He also asked the Lord to punish those who were persecuting him. But not only did he appeal to God’s promise; he also made one of his own: If God would rescue him, then he would tell the next generation about God’s power (see Ps 71:18).