4 But says some one: Ought the mind of the Christian to be troubled even at the prospect of death? For what comes of those words of the apostle, that he had a desire to depart, and to be with Christ, if the object of his desire can thus trouble him when it comes? Our answer to this would be easy, indeed, in the case of those who also term gladness itself a perturbation [of the mind]. For what if the trouble he thus feels arises entirely from his rejoicing at the prospect of death?
But such a feeling, they say, ought to be termed gladness, and not rejoicing. And what is that, but just to alter the name, while the feeling experienced is the same? But let us for our part confine our attention to the Sacred Scriptures, and with the Lord's help seek rather such a solution of this question as will be in harmony with them; and then, seeing it is written, “When He had thus said, He was troubled in spirit,” we will not say that it was joy that disturbed Him; lest His own words should convince us of the contrary when He says, “My soul is sorrowful, even unto death.” It is some such feeling that is here also to be understood, when, as His betrayer was now on the very point of departing alone, and straightway returning along with his associates, “Jesus was troubled in spirit.”
Source: Tractates on the Gospel of John (New Advent)