What to know
First, make sure that you're taking this question as having value and worth. Sometimes, when we hear a challenge to the Gospel, we can falsely assume wrong-intent: that the person isn't actually wanting to know, but is using the question as a set-up. Many of us are so familiar with the Bible, that we take parts of its narrative for granted, and we don't recognize some of the surprising aspects of its chapters. So before you speak, pause to reflect on the significance of the question...especially if (in your own faith), you've never struggled over the topic. To many Muslims, this is a significant barrier on the road to accepting the Gospel of Jesus, not just a "gotcha" attempt. Pause, take that in, pray, and then begin looking through how the Word of God speaks into this question. (Notice that aspects of this are similar to the overview for the question, "How did 'less than' become 'equal to'?") What to say
Read Matthew 8 and 9 (full chapters), Mark 2:1-11, and John 11 together.
What authority did Jesus have?
Ask your friend what stands out to them. Which of the miracles is the most surprising or confusing? Is the way that Jesus performed miracles surprising (or what you might expect from a prophet)? Why or why not?
Return to the question, but through a more specific lens: If Jesus had authority to do such great things...why did he pray?
Read John 14.
What words of Jesus stand out to you in this passage?
What words did Jesus use to express that He is One (the same in being) with God?
What words did Jesus use to express that he is in a submission-relationship to the Father?
Consider this apparent contradiction in human terms. Is a child of less value than an adult? Is a child of equal authority? As you say this, make sure to clarify that Jesus's claim that He and the Father are One is a statement that they're equal in value and worth, and equal in essence, in very being. (In this way, our analogy of human child and father falls short.) And yet, the question remains: Can two beings be equal (in value) and yet have different roles (of position and authority)? The holy Injeel says Yes: that Jesus was both equal to the Father and in a submission-role to Him...having been given a specific task to complete that He didn't turn from (Luke 9:51).
Tighten the question even further: If we rarely saw Jesus pray to the Father before providing a miracle...what was Jesus praying about? In what ways was Jesus in relationship to His Father?
Read Philippians 5:2-11, emphasis on verse 7-8.
What does it mean that God "emptied himself" when he took the form of a servant? What did Jesus empty himself of?
What privileges of being God did Jesus willingly give up?
In what ways was Jesus "fully man" (fully experiencing the weight of being a human) while on earth? What do you think that looked like and felt like?
Read Hebrews 2:14-18 and Hebrews 4:14-16.
Why is it significant that Jesus took on the experience of "suffering temptation"?
In what ways was Jesus, having emptied himself, dependent on God the Father while on earth?
Is prayer the only way that Jesus expressed that dependence and submission? Are there other moments from the passages above that come to mind?
Read Matthew 26 and Luke 22 together.
Before undergoing false accusation, physical torture, degradation, humiliation, and a painful death, Jesus - who knew what lie before him - poured out his heart to God. His anguish was so great that he "sweat great drops of blood." Yet during that prayer, he spoke the startling words, "My Father, if this cannot pass unless I drink it, your will be done."
The image we see of Jesus is absolute submission. While about to undergo the pain of becoming the Adha sacrifice, his desire was for the will of God to be done. He placed his own emotional and physical desires beneath the perfect and sovereign will of God. While still equal in essence and being, He showed what it means for the Father to be greater. The Father was in authority -- not emptied of anything at all; not weakened in any form; unable to even be tempted (James 1:13) -- and so his will was the highest desire of Jesus.
End with discussing how the terms the holy Injil gives us for the monotheism of God - Son, Father, and Holy Spirit - speak of a relationship of authority and submission, and ongoing presence in and among us today.
Jesus provided for us the perfect example of submission to God's will, and relationship to God the Father. This is incredibly important to all humans who want to please God. But Jesus's relationship to God was more than an example. Jesus experienced what it is to be a human, and accepted a weakened form. God is able to exist as the Father in Heaven and the Son of earth (and even dying on the cross) because He is all-powerful. He is One -- but he is One in a way that is much greater than what our human minds had imagined.
Read 1 Corinthians 2:8-10 together, and pray for God to reveal by his Spirit was is true.