“You will indeed drink from my cup, but to sit at my right or left ...” (Matthew 20:23)

“You will indeed drink from my cup, but to sit at my right or left is not for me to grant. These places belong to those for whom they have been prepared by my Father.” (Matthew 20:23)
Here is the situation:
Then the mother of Zebedee's sons came to Jesus with her sons and, kneeling down, asked a favor of him. "What is it you want?" he asked. She said, "Grant that one of these two sons of mine may sit at your right and the other at your left in your kingdom." "You don't know what you are asking," Jesus said to them. "Can you drink the cup I am going to drink?" "We can," they answered. (Matthew 20:22)
Apparently, Zebedee's sons were Jesus' disciples James and John - whom Jesus had recruited from a fishing boat on the Galilee shore.

What does Jesus mean by 'my cup' here?

Remember Jesus had just asked these two followers:
"Can you drink the cup I am going to drink?"(Matthew 20:22)
With that question and here again, the word "cup" is translated from the Greek word ποτήριον (potērion) which can mean "cup" or "drinking vessel" when used literally. However, we know that Jesus is not literally referring to a cup, as they were not currently drinking or sharing a cup. In other words, Jesus was using this word metaphorically.

When used metaphorically, this Greek word means "one's lot or experience, whether joyous or adverse, divine appointments, whether favorable or unfavorable" according to the lexicon.

This indicates that Jesus is using this word to indicate a broader sense of the word. He sees that the two are wanting to commit themselves to a life of service. They are desiring to make a change in their lives.

They were seeking to make a change from self-centeredness to loving God and loving others.

Can Jesus grant access to heaven?

Jesus clearly states that it is not his decision. He states:

"... but to sit at my right or left is not for me to grant."

Why would Jesus state this? Because, quite obviously, he is saying that he is not the Supreme Being, and thus he does not have the authority to decide who returns to the spiritual realm. 

So who makes the decision then?

"These places belong to those for whom they have been prepared by my Father.”

What does this verse mean by "places"? Is the spiritual realm some kind of award ceremony where everyone is assigned a particular seat and table to sit at? Don't be ridiculous.

What does Jesus mean by 'my right or left'?

The phrase "these places" has been inserted by some translators who do not understand the spiritual realm. They inserted it because of their misunderstanding of Jesus' metaphorical use of "my right" (ἐγώ δεξιός) and "my left" (εὐώνυμος). In fact, there is nothing indicating "these places" in the original Greek texts.

What Jesus is referring to as "my right" and "my left" are those who would become Jesus' associates within the spiritual realm. They would be associates because they would share in their service and love of the Supreme Being.

This is because the spiritual realm is outside the confines of the physical world where we wear these temporary physical bodies. There the inhabitants are engaged in loving service relationships with the Supreme Being.

Jesus is using metaphors to communicate a spiritual concept. To be at the right or left of Jesus means to be there in the spiritual realm with Jesus, also engaged in a loving relationship with God.

What does Jesus mean by 'prepared by my Father'?

The word "prepared" - coming from the Greek word ἑτοιμάζω (hetoimazō) - relates to preparations made in advance of someone's arrival. What kind of preparations are required for us to return to the spiritual realm? And how is the Supreme Being involved in that?

Jesus is speaking of redeveloping our relationship with the Supreme Being - which must be done in advance of our return to the spiritual realm. Does this mean God will be fluffing up some pillows in advance for us?

God is not our maid. Nor is He our genie where we can just ask Him to deliver up some stuff for us and He will do it.

Nor is the Supreme Being a thing. He is not a void or a monolith. The Supreme Being is a living person. He is the Supreme Person. Yes, He is more expansive and larger in every respect than ourselves and others. 

But each of us can still have a loving relationship with the Supreme Person.

The Supreme Being is already prepared. There is no preparation required on His part. It is we who need to become prepared.

A relationship is a two-way street. There are two people involved. If a boy wants to have a relationship with a girl he can't do it himself. The girl would also have to engage in that relationship in order for them to have a relationship.

In the same way, in order to redevelop our loving service relationship with the Supreme Being, we need Him to accept us back into that relationship. It is not that we can accept ourselves and just figure that we deserve to return to our relationship with Him and we are there.

But this doesn't happen automatically. We must consider that we were the ones who rejected the Supreme Being. We were the ones who decided that we didn't want to love and serve Him anymore. So He sent us away to the physical world and gave us these physical bodies to play out our self-centered desires.

But consider what it means to take someone back after being rejected. Consider a woman whose husband ran off with another woman and left her. Would she easily take the husband back after he cheated on her?

Certainly not. If she still loved him, she would want to make sure that the husband had changed his ways and wasn't going to leave her again. She would want to make sure that he was serious and really committed to returning to her. She would want to make sure he had a change of heart.

Does the Supreme Being need our commitment?

Right now we are cruising the physical world, looking for something that will satisfy us. God lets us do this because love requires freedom. But this world is also a place of learning. It is set up for us to learn and grow.

What does God want from us before we can return home to Him?

He wants to make sure that we are ready to return to Him. Yes, He loves us and wants us to return to Him. But not on a whim. He doesn't want us to whimsically return to Him, just to then decide again that we don't care about Him. The Supreme Being doesn't go for whimsical relationships.

He wants commitment. Just as any of us wants to have a commitment within a loving relationship.

The spiritual realm is full of committed loving relationships - each unique in that the Supreme Being has a specific type of loving relationship with each of us. In each loving relationship, the Supreme Being commits Himself to love us unconditionally: No matter what we do, He loves us and cares for us.

He simply wants the same in return. He wants us to love Him unconditionally. Not just because He gives us stuff. Not just because He takes care of us. He wants us to love Him no matter what. Jesus spoke specifically of this:
" 'Love the Lord your God with all your heart and with all your soul and with all your mind.' This is the first and greatest commandment." (Matt. 22: 37-38)
This is the nature of heaven. And this is why Jesus cannot grant the two boys their return to their relationship to the Supreme Being. It is between them and God.