'Unfit' in the Bible

But [like a boxer] I strictly discipline my body and make it my slave, so that, after I have preached [the gospel] to others, I myself will not somehow be disqualified [as unfit for service].

They profess to know God [to recognize and be acquainted with Him], but by their actions they deny and disown Him. They are detestable and disobedient and worthless for good work of any kind.