One of the more interesting aspects of Jesus’ interaction with the Samaritan woman at the well in John 4 is how the gospel writer weaves together the human and divine natures of Jesus Christ. He begins by highlighting how Jesus was tired from walking all morning and sought relief at Jacob’s well. In this description of our Lord, John highlights how he was susceptible to the weaknesses of humanity. In the beginning of John 4, then, we encounter the humanity of the Lord Jesus Christ.
And his humanity is utterly essential to maintain for many reasons. Most importantly, if the Lord Jesus, the one mediator between God and man, was not man, then he would not be able to represent man in his once-for-all sacrifice for sins. And thus, by extension, if he doesn’t completely represent us, i.e. he is not fully human, then he can’t fully redeem us, for as the early church fathers taught, “What is unassumed is unhealed.”
But John does not leave us in this episode with an exclusively human portrayal of the Messiah. Rather, at the critical moment of Jesus’ conversation with this Samaritan woman, he reveals his omniscience. If this woman were dealing with any ordinary teacher of the Law, the conversation would have been over when Jesus said, “Go, call your husband, and come here,” and she responded, “I have no husband” (4:16-17). But she was not dealing with an ordinary teacher of the Law but with the Word become flesh. Thus, Jesus indicates to her what he knows about her. His commendation of her factually true statement, in conjunction with his revelation that he knows her sketchy social past, communicates to her that her whole life is “naked and exposed to the eyes of him to whom we must give account” (Heb 4:13 ESV).
And this supernatural knowledge of her life, which highlights the divinity of the Messiah, being so closely connected with the exposition of the Messiah’s humanity, reinforces the church’s teaching that the Lord Jesus Christ is both fully God and fully man in one person. This close connection of humanity and divinity presses us to appreciate the uniqueness of the Lord Jesus as the only redeemer of God’s elect.
Now, the whole of the New Testament testifies to the full humanity and full divinity of the Lord Jesus. This truth is a central teaching of God’s revelation, even as it strains our ability to understand. Herman Bavinck puts it this way:
Though the image of the invisible God, the firstborn of all creation, he is nevertheless also the firstborn from the dead (Col 1:13-18); though son of David, he is simultaneously David's Lord (Matt 22:43); even though walking about on earth, he still continues to be “in the bosom of the Father” (John 1:18), “the one who is in heaven” (John 3:13), and existed before Abraham was (John 8:58); in a word, the fullness of deity dwells in him bodily. Every moment in Scripture, divine as well as human predicates are attributed to the same personal subject: divine and human existence, omnipresence and geographical limitation, eternity and time, creative omnipotence and creaturely weakness.
In this quote, the key is that the attributes and actions of both the divine and human natures are spoken of in regard to the one personal subject, the Lord Jesus Christ. Because people do things and not natures, the person, Jesus, is both tired and omniscient in the same encounter.
This doesn’t mean, though, that the Lord Jesus lived in a constant sort of bipolarism between his divine and human natures. Rather, in his one (divine) person, his two natures coexisted and cooperated appropriately and perfectly. One theologian has summed this up well like this:
Each nature in communion with the other performs acts appropriate to it, but performs them as acts of the one person who embraces both natures, and is the one subject of all the divine and human acts…It asserts a dynamic communion between the divine and human natures of Christ, in terms of his atoning and reconciling work. It stresses the union of two natures for mediatorial operations in such a way that these works proceed from the one person of the God-man by the distinct effectiveness of both natures.
And this observation is essential to our salvation, for the Messiah must be both God and man in order to save man, and he must be these things without confusion or without separation in order for his once-for-all sacrifice to be effective for us and for our salvation. In the end, John’s emphasis of both natures in this one story helps us to appreciate the fullness of Jesus Christ our Lord.
 Douglas Kelly, Systematic Theology (Christian Focus, 2014), 2:247.  Herman Bavinck, Reformed Dogmatics, ed. John Bolt, trans. John Vriend, 4 vols. (Grand Rapids: Baker Academic, 2003), 3:298-9.  T.F. Torrance, The Incarnation, 236, quoted in Kelly, Systematic Theology, 2:246.