55 Again, how great a mystery of word and act it is that Christ wept, that His eyes filled with tears from the anguish of His mind. Whence came this defect in His soul that sorrow should wring tears from His body? What bitter fate, what unendurable pain, could move to a flood of tears the Son of Man Who descended from heaven? Again, what was it in Him which wept? God the Word? Or His human soul? For though weeping is a bodily function, the body is but a servant; tears are, as it were, the sweat of the agonised soul.
Again, what was the cause of His weeping? Did He owe to Jerusalem the debt of His tears, Jerusalem, the godless parricide, whom no suffering could requite for the slaughter of Apostles and Prophets, and the murder of her Lord Himself? He might weep for the disasters and death which befall mankind: but could He grieve for the fall of that doomed and desperate race? What, I ask, was this mystery of weeping? His soul wept for sorrow; was not it the soul which sent forth the Prophets? Which would so often have gathered the chickens together under the shadow of His wings? But God the Word cannot grieve, nor can the Spirit weep: nor could His soul possibly do anything before the body existed. Yet we cannot doubt that Jesus Christ truly wept.
Source: On the Trinity (New Advent)