David was king, yet he knew that his strength did not come from his own hands. As a mighty warrior he understood the necessity of a strong fortress and a high tower with which to sight the approach of the enemy from afar. Yet these things were nothing apart from the Lord.
David knew his true fortress and his true high tower was God Himself! Even his shield was worth nothing apart from God! So much so that all of David's successes he attributed to the Lord and not himself.
What a great example for us to comprehend - that our true strength and power lies in God, and not ourselves. And, all we have to do to find, victory, joy, peace, and hope, is to trust in Him.
The Truth: “Trust in the Lord with all your heart, and do not lean on your own understanding. In all your ways acknowledge Him, and He will direct your path.”(Proverbs 3:5)