God asks nothing from us that He does not, in Christ, take upon Himself. There's nothing of love in demanding of someone else a task you yourself refuse to take on. The best reward still leaves that person only a valued employee - a good tool, but nobody loves a tool however useful it is. The situation Jeremiah finds himself in, of trusted friends now whispering and plotting against Him, Christ willingly accepts for Himself in the Gospel. Just a few days ago, in this same account, the men He is speaking to believed in Him. If He'd given them soft words, neither lying nor telling the full truth, they would still. But just as Jeremiah could not hold back from prophesying, neither can Christ restrain Himself; and now the crowd is ready to stone Him.
Christ defends Himself to the crowd on the basis of the works He has performed. They are not His but the Father's, and as such they stand in testimony to Him. He's speaking of His miracles, but it's all the more true of His work upon the Cross. Even when we find it hard to believe Him – we can believe that work. When we have no strength for anything else, we can still cling to the Cross.