Used to argue that Jews and Christians are expected to find Muhammad in their scriptures and then follow his rulings about what is lawful and unlawful.
Scripture spotlight
Quran 7:157-158
quran
157 those who follow the Messenger, 'the Prophet of the common folk, whom they find written down with them in the Torah and the Gospel, bidding them to honour, and forbidding them dishonour, making lawful for them the good things and making unlawful for them the corrupt things, and relieving them of their loads, and the fetters that were upon them. Those who believe in him and succour him and help him, and follow the light that has been sent down with him -- they are the prosperers.' 158 Say: 'O mankind, I am the Messenger of God to you all, of Him to whom belongs the kingdom of the heavens and of the earth. There is no god but He. He gives life, and makes to die. Believe then in God, and in His Messenger, the Prophet of the common folk, who believes in God and His words, and follow him; haply so you will be guided.'
Quoted to argue that the Quran itself claims Muhammad is written in the Torah and Gospel; this served as the launching point for the Isaiah 42 argument.