Jeremiah 1:4,5 - Joseph Benson’s Commentary on the Old and New Testaments

Then the word of the Lord came unto me With a satisfying assurance to himself, that it was the word of the Lord, and not a delusion. Before I formed thee in the belly That is, the womb. Having spoken before on the time of his call, he now speaks of the manner of it. I knew thee That is, I had thee in my view, or approved thee as a fit minister for this work, in the same sense as it is said, Acts 15:18, Known unto God are all his works from the foundation of the world; he contemplated the plan of them, and approved it in his mind, before he created and brought them into being. I sanctified thee I set thee apart in my counsel for executing the office of a prophet. We have examples of a similar designation with that mentioned here, in John the Baptist and St. Paul, as the reader will see if he consult the texts referred to in the margin. And ordained thee a prophet unto the nations He speaks thus to Jeremiah, not to the other prophets, because he stood in need of greater encouragement than they, both in respect to the tenderness of his years, and the difficulties which he was to encounter. And ordained thee a prophet to the nations To other nations besides the Jews.