Jesus was not mentioned by Greek or Roman sources in the first 100 years. And, his first Greco-Roman reference was a passing reference. Paul also tells us very little about what Jesus specifically said. Our earliest sources are the four gospels. They are not particularly reliable, but that doesn’t mean they are useless. The Gospels are not first-hand testimony, but people reporting hearsay. They couldn’t know Jesus’s exact words.
We can look at which testimony is earlier, whether one seems to be emphasizing a bias or a message rather than just telling us what happened, to what extent different sources agree with each other, and the extent that Jesus is saying something that seems like his followers would not want him to say.
Luke doesn’t see Jesus’s death as a sacrifice so God will forgive humans for their sins, but rather a key example of how sinful humans are–they killed God’s prophet! If you want to be forgiven, you have to turn back to God, but don’t need a sacrifice, according to Luke.
A version of Christian nationalism believes that Christianity is a pro-war religion that supports strong nationalist policies that protect Christianity and what it views as traditional life. It is more focused on defeating the enemy than on love. It is more about militaristic and capitalist ideology, than the words of Jesus in the Bible.