Chasidut su Proverbi 23:23

I was told that on one occasion the Rebbe spoke a great deal about the verse, “Buy the truth but do not sell it” (Proverbs 23:23). He asked: If the verse says not to sell the truth, then from whom should one buy it? Is it logical that the verse should say first, “Buy the truth” and then say, “but do not sell it”? If the verse says that no one should sell the truth, then whom should one buy it from? He spoke about this at length, but I did not hear what he said.