Adam Clarke on Psalms 34:19

Many are the afflictions of the righteous - No commander would do justice to a brave and skillful soldier, by refusing him opporbunities to put his skill and bravery to proof by combating with the adversary; or by preventing him from taking the post of danger when necessity required it. The righteous are God's soldiers. He suffers them to be tried, and sometimes to enter into the hottest of the battle and in their victory the power and influence of the grace of God is shown, as well as their faithfulness.

Delivereth him out of them all - He may well combat heartily, who knows that if he fight in the Lord, he shall necessarily be the conqueror.