We all know people who pretend to be something they’re not. They're contemptible.
He acts and speaks without pretense, with the calm assurance of absolute sovereignty. For example, multiple times in the Sermon on the Mount, He says, You have heard it said...but I say to you. (Compare Matthew 5:21-22, 27-28, 33-34, 38-39, 43-44). Christ is saying that His own word supersedes Jewish tradition and established interpretation of Scripture.
Or like the start of His ministry in His hometown of Nazareth. He read an 800-year-old prophecy about the Messiah who would preach good news to the poor, liberty to captives, recovery of sight to the blind, and freedom to the oppressed. (See Luke 4:16ff). Then He sat down and said, in effect, Today this prophecy is fulfilled--by Me (vv. 20-21).
Making claims like this is repugnant in weak, pretentious people. We pity, resent, and despise those who try to appear superior. We see that they are unqualified and unworthy.
But when Jesus speaks and acts as the King, we believe Him. When He tells us the secret of happiness, as He does in the Beatitudes, it rings true. When He says, "your tradition says one thing. But I'll tell you the truth," He is more than credible. He is compelling.
He's the real deal.