If Jesus is God, why in Mark 10 does Jesus reply “Why do you call Me good? No one is good but God” in response to someone asking, “Good teacher, what should I do to inherit eternal life?”
Excellent question. Here, Jesus is, of course, speaking as a human being. Notice that he is addressed as “good teacher,” and so responds according to what his human nature would prompt him to say. The word God, in Jesus’ day and in a Jewish context, meant only Yahweh/the heavenly Father. It did not mean the Trinity, much less the Second person of the Trinity. You could rephrase this “No one is good but the Father alone.” Jesus is not denying he is divine. He is denying he is the Father, or Yahweh, who in the first instance is the source of all goodness. In his divine nature, Jesus was one with the Father, but in his human nature he was distinguishable from the father and could speak in purely human terms.
—Ben Witherington III