1)
What is the meaning of "bEi'lokim Ahalel Devaro"?
1.
Rashi: Even when He comes against me with Midas ha'Din, I praise His word and trust in Him.
2.
Radak: The prefix Beis in bEi'lokim shows that this is connected to "Evtach" in the previous verse. I trust in Elokim, and praise His word that he said to me via Shmuel, that I will reign. I know that he will fulfill His word to me, even though I am pursued and exiled from place to place.
3.
Malbim: Refer to 56:5:2:1.
2)
Why does he not fear?
1.
Malbim: (a) It is due to His word. He promised me kingship; He is not a man to falsify His word. (b) I trust in Hashem; He saves all who trust in Him.