My flesh hath trembled for fear of thee. [1] At first sight the prophet seems to contradict himself. He had just now said, that, by God's severity, he was gently drawn to love his testimonies; now he declares, that he was seized with terror. But although these two effects differ widely from each other, yet, if we consider by what kind of discipline God forms us to reverence his law, we will perceive that they entirely harmonize. We require to be subdued by fear that we may desire and seek after the favor of God. Since fear, then, is the beginning of love, the prophet testifies, that he was awakened by a heart-felt fear of God to look well to himself. Nor is the mortification of the flesh so easy a matter, as that every one should consent to enter upon it, without the constraint of violent means; and, therefore, it is not wonderful if God struck his servant with terror, that, in this way, he might bend his mind to a holy fear of him. It is an evidence of no common wisdom to tremble before God when he executes his judgments, of which the majority of mankind take no notice. We are then taught by these words of the prophet, that we ought to consider attentively the judgments of God, that they may not only gently instruct us, but that they may also strike us with such terror as will lead us to true repentance.

Footnotes

1 - The verb smr, samar, rendered hath trembled, denotes being seized with horror, so that the hair stands on end. It occurs in Piel in Job 4:15. This state of horror was produced on the mind of the Psalmist by a contemplation of the divine judgments executed on the wicked, who are rejected like dross; and he was thus brought to fear God.

My flesh trembleth for fear of thee - I stand in awe of thee. I shudder at the consciousness of thy presence. See Habakkuk 3:16; Hebrews 12:21; Joel 2:10; Nahum 1:5. There is nothing unaccountable in this. Any man would tremble, should God manifest himself to him as he might do; and it is possible that the mind may have such an overpowering sense of the presence and majesty of God, that the body shall be agitated, lose its strength, and with the deepest alarm fall to the earth. Compare Daniel 10:8; Revelation 1:17. No man could meet one of the departed dead, or a good angel, without this fear; how much less could he meet God!
And I am afraid of thy judgments - Of thy laws or commands. My mind is filled with awe at the strictness, the spirituality, the severity of thy law. Reverence - awe - is one of the essential elements of all true religion.

My flesh trembleth for fear of thee - I know thou art a just and holy God: I know thou requirest truth in the inner parts. I know that thou art a Spirit, and that they who worship thee must worship thee in spirit and in truth; and I am often alarmed lest I fall short. It is only an assurance of my interest in thy mercy that can save me from distressing fears and harassing doubts. It is our privilege to know we are in God's favor; and it is not less so to maintain a continual filial fear of offending him. A true conception of God's justice and mercy begets reverence.

My flesh (f) trembleth for fear of thee; and I am afraid of thy judgments.
(f) Your judgments not only teach me obedience, but cause me to fear, considering my own weakness which fear causes repentance.

My flesh trembleth for fear of thee,.... Not for fear of the wrath of God coming down upon himself, nor for fear of eternal damnation; but for fear of what was coming upon the wicked, for their sins and transgressions. The word (n) used signifies such a dread and horror, which seizes a man to such a degree, that it makes the hair of his flesh to stand up; as Jarchi and Kimchi observe; see Psalm 119:53, Job 4:14;
and I am afraid of thy judgments; not of their coming down upon him, but upon the wicked; the thought of which is more awful to good men than to the wicked themselves; and especially when under any darkness, doubts, and fears; lest, being conscious to themselves of their own weakness, they should be left to join with the wicked in their sins, and so be partakers of their plagues.
(n) Symmachus in Drusius; "horripilavit", Cajetanus apud Gejerum.

The "judgments" are those on the wicked (Psalm 119:119). Joyful hope goes hand in hand with fear (Habakkuk 3:16-18).