Charles H. Spurgeon on Psalms 124:2

If it had not been the LORD, etc. This repetition is not in vain. For whilst we are in danger, our fear is without measure; but when it is once past, we imagine it to have been less than it was indeed. And this is the delusion of Satan to diminish and obscure the grace of God. David therefore with this repetition stirreth up the people to more thankfulness unto God for his gracious deliverance, and amplifies the dangers which they had passed. Whereby we are taught how to think of our troubles and afflictions past, lest the sense and feeling of God's grace vanish out of our minds. —Martin Luther.