All things work together for good.

This expression work together refers to medicine. Several poisonous ingredients put together, being tempered by the skill of the apothecary, make a sovereign medicine, and work together for the good of the patient. So all God’s providences being divinely tempered and sanctified, do work together for the best to the saints. He who loves God and is called according to His purpose, may rest assured that every thing in the world shall be for his good. This is a Christian’s cordial, which may warm him — make him like Jonathan who, when he had tasted the honey at the end of the rod, his eyes were enlightened (I Sam. xiv. 27). Why should a Christian destroy himself? Why should he kill himself with care, when all things shall sweetly concur, yea, conspire for his good? The result of the text is this. All the various dealings of God with His children, do by a special providence turn to their good. All the paths of the Lord are mercy and truth unto such as keep his covenant (Psalm xxv. 10). If every path has mercy in it, then it works for good.

A Divine Cordial by Thomas Watson (ca. 1620-1686)