Since Jesus claimed the Father is greater than Him in John 14:28, how can He be God?
Simply because one is greater than others in some respect is no reason to think they are not equal in other respects. The President of the United States is greater than the individual citizens in terms of his authority, but he is still equal to the citizens in terms of their nature—they are all human.
When it comes to the nature of God, the Bible is clear that Jesus has always had this nature. The Word was God from the beginning, and He created everything that was ever created (Jn. 1:1-3). Even in the context of John 14, Jesus said that if you've seen Him, you've seen the Father, and Jesus goes on to say that you can pray directly to Himself (9-14--some modern versions have picked up on the Greek term for "me" in verse 14). So the Father and Son are equal here (cf. Jn. 5:18-23, 10:30-33, 17:5 with Isaiah 42:8 and 1 Corinthians 2:8)… even if the Father is greater in terms of His position.
If this is true for the divine nature, then it is certainly true when it comes to the Son’s human nature as of 2,000 years ago. The Word of God, who was God from the beginning, humbled Himself when He took on a human nature (Philippians 2:5-10 and Hebrews 2:6-18). He became weak for our sakes. He was tempted, got hungry and thirsty, grew in wisdom and stature (Luke 2:52), and eventually was killed. None of these things are possible for God to do within His divine nature. Nonetheless, it is certainly possible for God to wire to Himself another nature in order to accomplish these things. So God the Father certainly is greater than the Son in terms of the latter’s human nature.
R. M. Sivulka
President, Courageous Christians United