John Calvin Commentary Psalms 118:18

"Jehovah hath chastened me sore; But he hath not given me over unto death." — Psalms 118:18 (ASV)

In chastising God has chastised me. In these words David acknowledges that his enemies assailed him unjustly, that they were employed by God to correct him, and that this was fatherly chastisement, with God not inflicting a deadly wound, but correcting him in measure and in mercy. He seems to anticipate the perverse decisions of perverse men which severely pressed upon him, as if all the troubles he had endured were so much evidence of his being cast off by God. He interprets these slanders which the reprobate cast upon him very differently, by declaring that his correction was gentle and fatherly. The main thing in adversity is to know that we are brought low by the hand of God, and that this is the way he takes to test our allegiance, to arouse us from our lethargy, to crucify our old man, to purge us from our filthiness, to bring us into submission and subjection to God, and to prompt us to meditate on the heavenly life.

If we remembered these things, every one of us would shudder at the thought of complaining against God, and would instead readily submit to him with a gentle and humble spirit. Our champing at the bit and rushing forward impatiently certainly stems from most people not viewing their afflictions as God’s rods, and from others not perceiving his fatherly care. The last clause of the verse, therefore, deserves particular attention: that God always deals mercifully with his own people, so that his correction proves to be their cure. Not that his fatherly care is always visible, but that in the end it will be shown that his chastisements, far from being deadly, serve as a medicine, which, though it may cause temporary weakness, rids us of our illness and makes us healthy and strong.