Psalm 70 - Prayer for divine help

The words of this short psalm are almost the same as the closing verses of Psalm 40. It is likely that there is a link between them, but there are some small differences, and they must be the reason why both psalms are included in the Psalter.

David, once again, is facing strong opposition and he turns to God in urgent prayer, asking him to come quickly and deliver him, otherwise his opponents may take his life. They do not think much of David and treat him with contempt. The circumstances are such in that the only One who can help David is the Lord. Yet if he should come to David’s aid, it is inevitable that David will be delivered because the Lord cannot be defeated (vv. 1-3).

David is not only concerned about himself. He also considers God’s people, those in Israel who looked to the Lord and sought fellowship with him. David wants them to have spiritual encouragement, to have assurance that the Lord can reveal his power, which is what would happen if he helped David. Such assurance would led to them affirming with joy the greatness of God (v. 4).

In order for that to happen, David cries to God to act. David has no personal resources that he can use. This fact he confesses to God, the One who has helped him in the past. Again, he implores God to come quickly and rescue him (v. 5). 

This psalm reminds us that God sometimes chooses to include similar chapters in his word. Psalm 18 and 2 Samuel 22 are very alike. So are Psalms 14 and 53. The compilers of the psalter would have known that most of Psalm 70 is found in Psalm 40. Maybe the answer is that the verses that make up Psalm 70 were regarded as suitable for use when making the particular offering mentioned in the heading of the psalm. 

Or it could be that sometimes a short prayer, which is what this psalm is, is more suitable for a believer to use than a longer one. In times of trouble, we can mention briefly but urgently to God our own needs, the needs of fellow believers, and the actions and attitudes of opponents, and then wait for God to answer.