This is a very common objection you will hear from Jehovah’s Witnesses when they come to your door. They will cite a verse like John 14:28, where Jesus says, “You heard me say to you, ‘I am going away, and I will come to you.’ If you loved me, you would have rejoiced, because I am going to the Father, for the Father is greater than I.”
Here is an explicit admission from Jesus of an inequality between him and the Father. From this admission, Jehovah’s Witnesses conclude the inequality is in God’s nature. Namely, the Father is God and Jesus isn’t. However, this assumes what needs to be proved. We need to ask, how is the Father greater than the Son?
This passage can be understood another way that makes sense of the whole of Scripture. Jesus is saying that he is subordinate to the Father. That is to say, the Father is greater in office, not in his nature.
Here is how I illustrate this with Jehovah’s Witnesses. In the biblical marriage relationship (which the JW agrees with), the husband and wife have different roles. Not only that, but the husband has a greater office than the wife. After all, he is the head of the family (Eph. 5:23). This might be controversial to secular society, but it shouldn’t be to a Jehovah’s Witness. So, in one sense, the husband is greater than the wife. However, in another sense, husbands and wives are equal because they both have the same human nature. They are equal in nature, but unequal in roles.
The marriage relationship is a dim reflection of God’s being. The co-equal, co-eternal Persons of the Trinity are one in divine nature. However, the Son submits to the Father in taking on human flesh and giving his life on the cross.
Furthermore, this makes sense of John 10:27-30. Jesus said: “My sheep hear my voice, and I know them, and they follow me.  I give them eternal life, and they will never perish, and no one will snatch them out of my hand.  My Father, who has given them to me, is greater than all, and no one is able to snatch them out of the Father's hand.  I and the Father are one.”
Many of us jump right to verse 30. But don’t miss the significance of verses 28 and 29. Whose hand are the sheep in? Are they in the Son’s hand, or are they in the Father's hand? Verse 30 solves the dilemma. The Son and the Father are one is divine nature; therefore, they are in God’s hand.
Scripture must be taken as a whole. “I and the Father are one” and “the Father is greater than I” must be understood together. A proper understanding of the Trinity makes sense of this.