Have you ever noticed how the New Testament writers sometimes express an important truth by saying what it isn't rather than what it is? That's "litotes" at work. You use this figure of speech when you want to make a positive affirmation by negating its opposite. It's often used for emphasis or to create a particular effect (such as irony). It can also serve to highlight a certain quality while denying its opposite:
"With God, nothing is impossible."
"The battle is not to be avoided."
"It's not warm today."
"He's not a bad cook."
"I'm not averse to the idea."
In Heb. 4:15 -- a verse I am committing to memory today in Greek -- Paul is saying something profoundly important but he's doing so with purpose and rhetorical skill.
Instead of just saying, "We have a high priest who is able to sympathize with our weaknesses," he chooses to express this truth by asserting the exact opposite. The combination of the negative "we do not have" with the negative "who is not able" creates a positive. The technique is designed to make the reader think more deeply about the statement.
And indeed, it's an amazing thought!
Ponder it. Christ not only suffers with his people. He identifies with their weaknesses. He is "not without concern" (to use a litotes!) for us in our lowly condition. Having been made flesh, the Son of Man himself experienced all the temptations and infirmities common to man, sin excepted. He is therefore abundantly qualified to sympathize with us in our afflictions. As God, he is infinitely holy. As man, he is infinitely compassionate. He knows the difficulties of living righteously in this world. I love how Phillips captures this amazing truth:
"For we have no superhuman High Priest to whom our weaknesses are unintelligible."
And here's the way Eugene Peterson has rendered the verse:
"We don't have a high priest who is out of touch with our reality."
God says, "You must be holy because I am holy." On our own, that's as impossible to attain as growing another foot in height after reaching adulthood. The good news is that God in Christ is at work in us, giving us both the desire and the ability do what pleases him. It's just a matter of allowing him enough elbow room to do his work!
Have a wonderful day!