In chapters 71-80 of Justin's dialogue with Trypho, he mostly goes into repetitions about Scriptures that the Jewish people ignore. He appeals to some Apocryphal works that I agree do not have any more spiritual inspiration than some book from Barnes and Noble. But it is telling that when the Dead Sea Scrolls were discovered nearly 60 years ago, that missing verses showed up in certain Psalms that most certainly point to Jesus. The Jews are not impressed with them and prefer to not have them.
Trypho seems to finally take Justin seriously. He asks a good question. If Christ is pre-existent, then why do the Scriptures speak of the Spirit resting on him? Justin answers that his powers came upon him not because he needed them, but because they find their accomplishment in him. Prophecy and signs climax in Jesus and fizzle out shortly after the apostles die. None of the signs: the virgin birth, riding into town on a donkey, the temptation in the desert: none of them made him Christ. They showed that he was Christ.
Slowly, Trypho and his buddies concede, but they still can't wrap their mind around the need for Christ to die a crucifixion since it comes with a curse. All the same, says Justin, the Scriptures prophesy just that. It is even typified by Moses when he stretches out his hands so that Israel will win against Amalek. That is a type of the cross. It happened while Joshua (same name as Jesus) led Israel as commander.
What can we reap from all this dialogue? Maybe if we chisel away at unbelief enough, those we wish to persuade will finally understand, or at least will come to a peace about what can't be understood. Sometimes, people we love still won't get our point even with much concrete proof in Scripture and in nature. Trypho still doesn't get the crucifixion. People today still won't reorganize their mind to leave the evolutionary brainwashing we all received in school and be free to not compromise their beliefs in God. They could be free to simply take God at his word, but they still get bogged down in the forest by the trees. No matter. Our goal is not to convert them. Our goal is to continue to open their hearts to Scripture so that Jesus can finally convert them.