The answer to this question hinges on how trinitarians understand the incarnation of Christ. And while there is broad (though not quite universal) agreement with the Chalcedonian Definition (451), and its statements that Christ is "truly God and truly Man" with two natures that are joined "unconfusedly, unchangeably, indivisibly, [and] inseparably" in one person, there is still disagreement on the particulars of how this incarnation should be understood:
- Does Christ have one united nature (miaphysitism; held by Oriental Orthodox), or two distinct natures (dyophysitism, as per Chalcedon)?
- Does Christ have one will (monothelitism), or two (the view of the Third Council of Constantinople (680–681))?
- What kind of connection exists between Christ's human nature and his divine nature, or, put another way, in what sense did he "empty himself" (Phil. 2:7)?
For now, we'll focus on the last of these points, which is where debate today is largely centered. Three positions stand out, which I'll attempt to summarize first before expanding on them:
- Catholicism: Christ, through the incarnation, has much divine knowledge, but not elements (like this one) that are irrelevant to his ministry.
- Reformed theology: The development of Christ's knowledge largely parallels that of a normal human's, because he does not will to obtain more divine knowledge than is needed – such as the date of his return.
- Kenotic theology: Christ divests himself of omniscience in the incarnation, so this knowledge is not available to him.
The Catechism of the Catholic Church, §464–480, first lays out some of the historical context for this issue, then describes the Church's view of Christ's incarnation. The most relevant sections are §472–74, where we first see how Christ "learned" while on earth:
This human soul that the Son of God assumed is endowed with a true human knowledge. As such, this knowledge could not in itself be unlimited: it was exercised in the historical conditions of his existence in space and time. This is why the Son of God could, when he became man, "increase in wisdom and in stature, and in favour with God and man", and would even have to inquire for himself about what one in the human condition can learn only from experience. This corresponded to the reality of his voluntary emptying of himself, taking "the form of a slave". (§472)
However, the knowledge of Jesus was more extensive than a typical human's. His human nature "knew and showed forth in itself everything that pertains to God," such that he had "intimate and immediate knowledge" of his Father and had "divine penetration" into the secret thoughts of men (§473). But this knowledge had limits – it only included what was intended for him to reveal:
Christ enjoyed in his human knowledge the fullness of understanding of the eternal plans he had come to reveal. What he admitted to not knowing in this area, he elsewhere declared himself not sent to reveal.
In contrast, Reformed theology generally criticizes the Roman view for believing that the incarnation in itself resulted in Christ having so much divine knowledge – thus implying that he had it all from birth. Instead it generally holds a "purely human development of Christ" (Bavinck, II, §357), as Mark Jones explains:
He developed from infancy into manhood, and experienced a growth in knowledge that was appropriate to his stage in life. He had to be taught by his Father. He had to content himself that not everything was revealed to him during his time on earth. He 'learned obedience' through suffering. He learned of his future sufferings through reading the Old Testament Scriptures. We must secure room for a purely human development in the life of Jesus in order to do justice to the Scriptures and Christ's human nature. (Knowing Christ, 46–47)
But this does not negate the fact that Jesus did demonstrate some divine knowledge. J. I. Packer writes:
The reason why He was ignorant of (for instance) the date of His return was not because He had given up the power to know all things at the incarnation, but because the Father had not willed that He should have this particular piece of knowledge while on earth. [...] So Jesus's limitation of knowledge is to be explained, not in terms of the mode of the incarnation, but with reference to the will of the Father for the Son while on earth. (Knowing God, chapter 5)
The Greek word kenosis is crucial to this question, as it comes from Philippians 2:7, where Jesus is said to "empty himself" in the incarnation. Thus in a sense all trinitarians believe in some form of "kenosis," but not in the same way. Modern Kenotic theology, first developed in the late 19th century, is a new approach that in only some of its varieties attempts to stay within trinitarian orthodoxy.
In Kenotic theology, we see a defined "self-limitation" on the knowledge of Christ, often to the extent that Christ divested himself of the divine attribute of omniscience while on earth:
Kenotic theology [argues that] in the incarnation, however conceived, there was a preincarnate act of limitation, whether it be a "laying aside" (Charles Gore) or a "concentration" (P. T. Forsyth). (Evangelical Dictionary of Theology, 652)
A primary driver for the development of this theory was to allow for the full humanity of Christ, in light of higher criticism. For example, Christ's high regard for the accuracy of the Old Testament can be safely discarded if he is understood to have learned this from his Jewish upbringing, not as a matter of divine knowledge. (On this, see J. I. Packer, Knowing God, chapter 5)
Thus in this view it becomes obvious that Christ couldn't know the date of his return, but at the same time its proponents face the criticism that they have denied the full divinity of Christ.
The distinctions between these three views might seem rather tricky, but one way to more clearly see the differences is to focus on what happens in the incarnation itself. Attempting to summarize:
- In Catholicism, Christ has all relevant divine knowledge in his person by virtue of the incarnation itself.
- In Reformed theology, Christ's incarnation with two natures means that in his person he has access to divine knowledge, if it be God's will, but generally his knowledge develops normally.
- In Kenotic theology, Christ's incarnation involves a loss or rejection of divine knowledge, so in his person he does not have access to it.
Thus we see that this matter, like many others dealing with the trinity, is much debated, even among trinitarians!