Commentaries:
Barnes' Notes
For I said - This is the prayer to which he referred in the previous verse. He prayed that he might not be permitted to fall away under the influence of his sins and sufferings; that his faith might remain firm; that he might not be allowed to act so as to justify the accusations of his enemies, or to give them occasion to rejoice over his fall. The entire prayer Psalms 38:16-18 is one that is based on the consciousness of his own weakness, and his liability to sin, if left to himself; on the certainty that if God did not interpose, his sins would get the mastery over him, and he would become in his conduct all that his enemies desired, and be in fact all that they had falsely charged on him.
Hear me, lest otherwise they should rejoice over me - literally, "For I said, lest they should rejoice over me." It is the language of earnest desire that they might "not" thus be allowed to rejoice over his fall. The same sentiment occurs substantially in Psalms 13:3-4. The motive is a right one; alike
(a) in reference to ourselves personally - that our foes may not triumph over us by the ruin of our character; and
(b) in reference to its bearing on the cause of virtue and religion - that that cause may not suffer by our misconduct; compare Psalms 69:6.
When my foot slippeth -
(a) When my foot really has slipped, or when I have committed sin (as the psalmist did not deny that he had done, Psalms 38:3-5, Psalms 38:18); or
(b) when it "might" occur "again" (as he felt was possible); or
(c) if I deviate in the slightest degree from perfect virtue; if I inadvertently do anything wrong.
The slipping of the foot is an indication of the want of firmness, and hence, it comes to represent the falling into sin.
They magnify themselves against me - See Psalms 35:26. They exult over me; they triumph; they boast. They "make themselves great" on my fall, or by my being put down. This he says
(a) they were disposed to do, for they had shown a disposition to do it whenever he had fallen into sin;
(b) he apprehended that they would do it again, and they had already begun to magnify themselves against him, as if they were certain that it would occur.
He did not deny that there was ground to fear this, for he felt that his strength was almost gone Psalms 38:17, and that God only could uphold him, and save him from justifying all the expectations of his enemies.
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