John Calvin on John 17:13

13. And these things I speak in the world. Here Christ shows that the reason why he was so earnest in praying for his disciples was, not that he was anxious about their future condition, but rather to provide a remedy for their anxiety. We know how prone our minds are to seek external aids; and if these present themselves, we eagerly seize them, and do not easily suffer ourselves to be torn from them. Christ, therefore, prays to his Father in the presence of his disciples, not because he needed any words, but to remove from them all doubt. I speak in the world, says he; that is, within their hearing, or, in their presence, “En leur presence.” that their minds may be calm; for their salvation already was in no danger, having been placed by Christ in the hands of God.

That they may have my joy fulfilled. He calls it HIS joy, because it was necessary that the disciples should obtain it from him; or, if you choose to express it more briefly, he calls it his, because he is the Author, Cause, and Pledge of it; for in us there is nothing but alarm and uneasiness, but in Christ alone there is peace and joy.

John 17:14-19

14. I have given them thy word, and the world hath hated them; because they are not of the world, even as I am not of the world. 15. I ask not that thou shouldest take them out of the world, but that thou shouldest keep them from the evil. 16. They are not of the world, even as I am not of the world. 17. Sanctify them by thy truth: thy word is truth. 18. As thou hast sent me into the world, I also have sent them into the world. 19. And for their sakes I sanctify myself, that they also may be sanctified by the truth.