If I said, My foot has fallen What is said in this verse confirms the preceding statement. The more to commend God's kindness and power, he declares that it was no common danger from which he had been rescued, but in a manner from present death. The import of the language is, that death stared him so full in view, that he despaired of himself; as Paul speaks of having had the message of death in himself, when his condition was desperate, and he had given up hope of life, (2-Corinthians 1:9.) The fact of the Psalmist having been delivered after he had considered death certain, made the Divine interposition the more conspicuous. If we understand him as speaking of temporal death only in the expression, My foot has fallen -- there is nothing unaccountable in the circumstance of his having despaired, as God often prolongs the life of his people in the world, when they had lost hope, and were preparing for their departure. Possibly, however, the Psalmist only means that this was the language of sense; and this is the more probable, because we have already seen that he never ceased praying to God -- a proof that he had still some hope. The next verse affords still further proof, for there he tells us that his afflictions were always mixed with some comfort. By thoughts, he means anxious and perplexing cares, which would have overwhelmed him had not consolation been communicated to him from above. We learn this truth from the passage, That God interposes in behalf of his people, with a due regard to the magnitude of their trials and distresses, and at the very moment which is necessary, enlarging them in their straits, as we find stated in other places. The heavier our calamities grow, we should hope that Divine grace will only be the more powerfully manifested in comforting us under them, (Psalm 4:1; 118:5,) But should we through weakness of the flesh be vexed and tormented by anxious cares, we must be satisfied with the remedy which the Psalmist here speaks of in such high terms. Believers are conscious of two very different states of mind. On the one hand, they are afflicted and distressed with various fears and anxieties; on the other, there is a secret joy communicated to them from above, and this in accommodation to their necessity, so as to preserve them from being swallowed up by any complication or force of calamity which may assail them.

When I said, My foot slippeth - I can no longer stand. My strength is gone; and I must sink into the grave. The original here is, "If I say, My foot slippeth," etc. The statement is general; that if at any time he had been, or should be, in such circumstances, then God would interpose. The general remark, however, is founded on his interposition on this particular occasion. His aid was then so marked and timely, that he felt that he could make the declaration general in regard to his whole life - to all circumstances in which he would ever be placed.
Thy mercy, O Lord, held me up - By thy merciful interposition thou didst keep me from falling. It was strength put forth as the expression of "mercy;" not strength to which he had any claim. How often in life may we say this of ourselves, that when just ready to sink; when our strength was almost gone; when a little severer pressure would have brought us to the grave, God by his mercy and his power interposed and saved us! Every such act of mercy - every new interposition in this manner - is a new gift of life, and lays us under obligation as if we had been just created, for it is just so much more of life given us by God.

When I said, My foot slippeth - When I found myself so weak and my enemy so strong, that I got first off my guard, and then off my center of gravity, and my fall appeared inevitable: -
Thy mercy, O Lord, held me up - יסעדני yisadeni, propped me. It is a metaphor taken from any thing falling, that is propped, shored up, or buttressed. How often does the mercy of God thus prevent the ruin of weak believers, and of those who have been unfaithful!

When I said, (l) My foot slippeth; thy mercy, O LORD, held me up.
(l) When I thought there was no way but death.

When I said, my foot slippeth,.... There is no ground for me to stand upon; all is over with me; there is no hope nor help for me; I am just falling into ruin and destruction: such will be the desperate case of the church, at the time before referred to:
thy mercy, O Lord, held me up; the extremity of his people is the Lord's opportunity; then is his set time to arise, and have mercy on them; then mercy steps in, lays a solid ground and foundation for hope, and holds up in its arms a sinking people, and revives a dying cause.