Trial before the Sanhedrin
The context of Luke 22:70 is Jesus's trial before the Sanhedrin, so we need to consider the whole passage: Luke 22:66-71 (ESV):
⁶⁶ When day came, the assembly of the elders of the people gathered together, both chief priests and scribes. And they led him away to their council, and they said, ⁶⁷ “If you are the Christ, tell us.” But he said to them, “If I tell you, you will not believe, ⁶⁸ and if I ask you, you will not answer. ⁶⁹ But from now on the Son of Man shall be seated at the right hand of the power of God.” ⁷⁰ So they all said, “Are you the Son of God, then?” And he said to them, “You say that I am.” ⁷¹ Then they said, “What further testimony do we need? We have heard it ourselves from his own lips.”
We can see how the trial focused on Jesus's identity, which in fact one of the main themes of the whole book of Luke. Thus Luke's main task was to show through Jesus's dialogues, parables, teachings, miracles, etc. how key OT prophecies which pointed to Jesus (from where Jesus's many titles and roles came from) were not simply attributions by His followers but affirmed by Jesus Himself. These trials before the Sanhedrin and before Pilate are just one example of the narrative and dramatic vehicle he used.
Pulpit Commentary on Luke 22:66-70 explained how in v. 67 Jesus confronted the questioner that He already answered them in previous encounters, and with His healings and miracles the answer should have been accepted (see earlier chapters of Luke). Furthermore, Jesus already engaged them in OT disputation (see Matt 22:41-45) but they refused to "play ball", so Jesus reminded them of this (v. 68). Then in v. 69 Jesus volunteered the critical information that His interrogators were trying to find to frame him. Then in v. 70 they followed up on Jesus's voluntary self-identification as "Son of Man", asking Him for a clearer identity as "Son of God", to which Jesus simply answered "YES", but in a Rabbinic style response which the interrogator understood right away, proven by their response in v. 71.
Why does Jesus say "You say I am" and "You say so", when they haven't?
Answer: To the contrary, they understood the "Yes" that Jesus was saying, although they did not believe the answers.
Quote from the Pulpit commentary on verse 70:
Now bringing forward the loftier title formerly suppressed (in ver. 67). "And art thou, then, dost thou, poor Man, vain in thy imagining, dost thou assert thyself to be the Son of God?" So Stier. "And he said unto them, Ye say that I am." This form of reply is not used in Greek, but is frequent in rabbinic. By such an answer the one interrogated accepts as his own affirmation the question put to him in its entirety. We have, then, here, in the clearest possible language:
A plain assertion by our Lord of his Divinity.
The reply of the Sanhedrists, showing that they for their part distinctly understood it as such, but to make it quite clear they asked him if that was his meaning, i.e. the assertion of his Divinity.
We have the Lord's quiet answer, "Yes, that was his meaning." The next verse (71) shows that they were satisfied with the evidence which they proceeded without delay to lay before the Roman governor, Pilate.
Trial before Pilate
Luke 23:1-5, ESV:
¹Then the whole company of them arose and brought him before Pilate. ² And they began to accuse him, saying, “We found this man misleading our nation and forbidding us to give tribute to Caesar, and saying that he himself is Christ, a king.” ³ And Pilate asked him, “Are you the King of the Jews?” And he answered him, “You have said so.” ⁴ Then Pilate said to the chief priests and the crowds, “I find no guilt in this man.” ⁵ But they were urgent, saying, “He stirs up the people, teaching throughout all Judea, from Galilee even to this place.”
Joel Green's New International Commentary on the book of Luke noted the irony underlying both Pilate's question and the Sanhedrin's question in that both questioners had in fact identified Jesus correctly, but refused to believe Him:
- In the Sanhedrin's case it was hardness of heart (because they are Jews and unlike Pilate they knew precisely what Jesus's claim of identity meant for the Jewish religion).
- In Pilate's case, he thought Jesus was "a harmless eccentric", so not worth crucifying, because the punishment doesn't fit the "crime".
The way Jesus answered "yes" to them could then be construed as ironic affirmation because Jesus knew how both of them didn't believe the answers anyway. Luke included the dialog for the readers's benefit (including us) who do not have access to Jesus in person.
Here's a quote from Joel Green's commentary on Luke 23:3-4:
3-4 Although he will return to the primary charge brought against Jesus in v 14, in the Lukan narration Pilate now seizes on this last issue, formulating the charge in terms of Jesus’ royal status. Given the opportunity to answer the question whether he was “king of the Jews,” Jesus replies in a way that is reminiscent of his answer to the sanhedrin in 22:70. Here, as there, Jesus turns the question posed to him into an ironic affirmation about him—ironic because even though the question assesses Jesus’ identity correctly, it is an identity not granted by those who ask it. Why Pilate’s response is to dismiss the charges—for example, because he regards Jesus as innocent (in the judicial sense) or, say, a harmless eccentric—is not evident at this juncture.³⁵ In either case, neither Pilate nor the Jerusalem authorities regard Jesus as the one who rules God’s people.³⁶