For what does he always hope?
Rashi: Your salvation.
Radak: That You will save me, and I will be able to add to Your praise, over what I praised You for all the afflictions from which You saved me.
Malbim: Even though those who contest my soul will be eradicated, I will constantly hope to You. Hope for human help is only at a time of affliction. Hope to You is even when there is no adversary. It is not to fill a lack; rather, also continued success is from You! Success is not natural; it is via Hashgachah. Every moment of serenity is from You. I ask You to continue it.
When will he add to His praise?
Rashi: When He will save him, he will add. Radak - the last syllable of "v'Hosafti" is accented (this shows that the Vov switches it to the future).
Malbim: At every moment. I picture to myself as if all evils surrounded me (I am prone to every evil if You would remove Your Hashgachah for a moment), and You saved me. One who exists via nature, he adds praise only after a Tzarah comes, and he is saved from it. My entire existence is via Hashgachah; I receive a miracle every moment!
