And the flesh is that reprehensible preference for self that lurks within every one of our hearts. It is that base and selfish instinct to preserve our own interests at the expense of God's interests. It's devious, it's deceitful, it's self-indulgent. It's interested only in selfish comfort and will happily crucify Christ afresh to secure it. God also has another name for it- sin.
Either Jesus is the Son of God ; or a madman or worse. But His being just a great teacher? He's not left that open to us.