Under the soon-to-be-outdated Mosaic case-law, it was necessary to have two witnesses that agreed. The other Gospels point out that getting the Agreement was the hard part. Especially in this capital case, giving a false witness would result in execution for that witness. Yet here we had 'many', possibly eager for bribes from the chief priests, eager to risk it.  Now, thankfully, since the law has been abolished, we no longer need two or more witnesses to condemn men in court. Neither does their testimony need to be 'true'. Any kind of testimony will do now during this period where Jesus is not yet lawgiver, judge, nor king. We saw this played out in the Netherlands during the Protestant Reformation. Once you were accused (even anonymously) of having Protestant sympathies you could get off easy by just admitting your guilt. That way they would just bury you alive. If you refused to recant, that is when they would burn you at the stake.

This shows Christ's claim of the messianic Office of Priest. He is the Temple, the sacrifice on the altar, the priesthood who offers the pure worship, who cleanses the people for service via the laver, the Bread on the Table, the intercessory incense rising as a sweet savor to the Father, the Veil that connects us to the presence of God. In His prophesying of a future, sure event with risk of execution if He is a false witness, we see illustrated His messianic office of Prophet. These are the sure words of God the Prophet is passing on to us.

I've heard that the rule in the Sanhedrin, is that the high priest was not allowed to speak. Obviously, since he was regarded as the "supreme court chief justice", his opinion would be inordinately influential in swaying the opinion of the 'jurors'. And they are all watching an innocent man being falsely accused for the purpose of murdering him. They would know that they could be next if they didn't agree with the powers that be. And even more surely, the Accused could not be called upon to witness against himself. It was the job of the court to come up with their own evidence.

This is the Public Adjuration to testify in a court case, and if you were silent or gave a false witness -- God would, even if men could not manage to catch and punish you for false witness, bring down the guilt upon your head. We see this is a couple places:

Lev. 5:1 ‘Now if a person sins after he hears a public order to testify when he is a witness, whether he has seen or otherwise known, if he does not tell it, then he will bear his punishment.

Prov. 29:24 One who is a partner with a thief hates his own life; He hears the oath but tells nothing. The high priest is referencing at least three messianic passages: Dt. 18, Ps. 2 and 110. He is asking, if He is The Prophet, and The Son Begotten, anointed as emperor over all nations:

 

¹⁸ I will raise up for them a prophet from among their countrymen like you, and I will put My words in his mouth, and he shall speak to them everything that I command him. ¹⁹ And it shall come about that whoever does not listen to My words which he speaks in My name, I Myself will require it of him.

 

“But as for Me, I have installed My King

Upon Zion, My holy mountain.”

 

 

⁷ “I will announce the decree of the Lord:

He said to Me, ‘You are My Son,

Today I have fathered You.

⁸ Ask it of Me, and I will certainly give the nations as Your inheritance,

And the ends of the earth as Your possession.

⁹ You shall break them with a rod of iron,

You shall shatter them like earthenware.’”

 

 

Jesus voluntarily breaks protocol here and does actually testify. This is rare. In most other trial points (Herod, Pilate) He is like a lamb, silent before slaughter, not trying to defend Himself against the specific accusations. Many times in His ministry, He directed people, even demons, to NOT publicly identify Him as Messiah. This highlights the unusualness of His Testimony, and I believe this moment is what is referred to in other NT passages.

Rev. 1: "...His bond-servant John, ² who testified to the word of God and to the testimony of Jesus Christ, everything that he saw...⁵ and from Jesus Christ, the faithful witness.....⁹ I, John, your brother and fellow participant in the tribulation and government and perseverance in Jesus, was on the island called Patmos because of the word of God and the testimony of Jesus.

Here, Jesus owns the charge by referencing Ps 110, and Daniel 7

The Lord says to my Lord:

“Sit at My right hand

Until I make Your enemies a footstool for Your feet.”

 

“I kept looking in the night visions,

And behold, with the clouds of heaven

One like a son of man was coming,

And He came up to the Ancient of Days

And was presented before Him.

¹⁴ And to Him was given dominion,

Honor, and an empire,

So that all the peoples, nations, and populations of all ^[m]languages

Might serve Him.

His dominion is an everlasting dominion

Which will not pass away;

And His empire is one

Which will not be destroyed.

So now, they did not need any outside witnesses who couldn't keep their story straight. Both Annas, Caiaphas, and the entire Seventy were witnesses to Jesus's testimony. If His witness was true, then all His false accusers must die, because of their false accusation and trying to murder the Innocent. If His testimony was false, then He should die for the ultimate contumacy against all competing civil authority. This is highest treason possible. It is also possible they understood this as a claim to be Yahweh Himself, remembering His claim: "I and my Father are one."