David addresses here a problem that plagued Israel continuously, both before and after his reign. The key principle is this: any task attempted without the Lord is doomed to failure. In Israel’s case, these tasks more often than not manifested themselves as battles with neighboring lands. But God made it clear that He would not bless their refusal to obey—if He made it clear that they should not go into battle, or that certain conditions applied to any battle, His people should obey. If they did, success and victory would result, for He was with them. But if they disobeyed by embarking on their own, or trying to do things their own way, He would withdraw the blessing of His presence from them.
David acknowledges in this psalm that Israel has had to learn the hard way many times in the past. He humbles himself before the Lord, confessing that they had displeased God by their past actions, and asks for restoration. Then David reminds his readers and listeners of God’s promise—that Israel will claim the land for His glory. So he calls upon the Lord to be with them, for, as he says, “the help of man is useless.” David understood that men’s strength and power were useless. He, the physical Israel’s most famous king in the Bible, made it clear that it was God’s working through him. He did not allow his vanity and pride to get the best of him, but gave all the glory to God. He kept going back to the Lord as his source and his provider and his strength.
Likewise, even today God’s people must set their plans before the Lord, and be careful to obey all that He commands. Otherwise, their plans are also doomed to failure if they rely on the strength of men. But if those are formed from the promises of God, the method is in obedience to Him, and the enactment relies on His strength, it will prevail—guaranteed.