David, under the inspiration of the Holy Spirit, gave his last will and testament so to speak. In these last words he speaks of the wonderful things that God had done for him, and points forward with the everlasting covenant in verse 5, a covenant we know now points forward to his descendent, Jesus Christ.
The rest of the chapter tells of the deeds of David’s might men. My favorite is Benaiah, who went after a lion in a pit on a snowy day. Each prepositional phrase makes that task even more amazing and daring. Yet we remember from David’s psalm that each of these mighty men were really only God’s instrument, receiving the power and strength that God gives to them to do the task that was given them to do.
You probably will never face an actual lion in a pit on a snowy day, yet there are many difficult things we will face in our faith walk. And God encourages us to attack that difficult thing, not with your strength, but with His!