Verse 10 said "Uzo Elecha Eshmorah. Why does it say here "Uzi Elecha Azamerah"?
Radak: Above, he said that Sha'ul has strength against me, so I wait for You to help me against him. Now, after the salvation, I say Uzi (for You gave to me strength over him) Elecha Azamerah (I will sing; I need not wait for Your help).
Malbim: Above, Hashem promised to guard for David the strength of Sha'ul; later, it will be to David. Here he says, when it will be my strength, i.e. I will be king, I will sing to You.
Why did he say "Elokim Misgabi Elokei Chasdi"?
Radak: You are the Judge with all ability. You waged my case against them, and You leaned Your Chesed towards me, and then it is called my Chesed.
Malbim: Elokim is my refuge because He is G-d of my Chesed; kingship was given to me due to Chesed.
