These verses in Isaiah are describing Jesus’s trials before Caiaphas, Pilate, Herod, and the priests and elders, before he was crucified. Even though the charges they brought against him were unjust, He did not speak in defense of himself or refute the charges. Pilate even prompted Jesus to speak up for himself because he wanted to free him, but Jesus remained silent and did not argue on his own behalf.
The prophet Isaiah is not talking about himself. He is talking about Jesus Christ, the Messiah, who being God himself, came to earth in the form of a human. Jesus walked the earth, resisting Satan’s temptations, healing the sick, raising the dead, and casting out demons to disarm Satan and set humanity free from him. Earthly rulers feared Jesus and his power, and they believed that killing Jesus would prove their authority in the world. When these rulers brought unjust accusations against Jesus, he did not refute the accusations or speak on his own behalf, as you have read in Isaiah’s prophecy. Also, as Isaiah says in these verses, Jesus was unjustly accused and he was killed because of the sins of others. However, God demonstrated His divine power by raising Jesus from the dead, thus reclaiming all power and dominion from Satan. God sent His Son Jesus to live among His people and sacrificed Him on the cross, allowing Him to die in our place and for our sin, because of His great love for us. And Jesus didn’t die just for the Israelites but for everyone, including you. Through Jesus’s death and resurrection, God has restored you and brought you back into relationship with Him. That is the person the prophet Isaiah was talking about in these verses.