He shall not be afraid of evil tidings - Of bad news; of reverses and losses; of the destruction of his ship at sea, or his property by land; of disaster by flood, by famine, by war. His heart will so fully confide in God that he can commit all calmly into his hands. He will feel assured that all will be well; that nothing occurs but that which the wisest and the best Being in the universe sees it best should occur; and that in all which “does” take place he is able to sustain the sufferer. There is nothing so well suited to make the mind calm as trust in God. What has a man to be afraid of who does trust in him? Compare Psalms 27:3; Psalms 46:2; Psalms 56:3-4; Hebrews 13:6; Proverbs 1:33.
His heart is fixed - Is firm; is established. See the notes at Psalms 57:7.
Trusting in the Lord - This is the reason “why” his heart is “fixed” or firm. It is not any native courage or resolution; it is not any firmness of his own; it is simply because he has confidence in God, and feels assured that all things will be well.