Many receive the knowledge of the truth (salvation by Christ) into the mind, but not into the heart. This is were the error lies in Gnosticism, for they believed that merely knowing about salvation was to be saved (of course not suspecting you here).
Please compare how this word is used in context in the following verses, as
"head knowledge" is not implied at all.
26 For if we sin willfully
after we have received the knowledge [1922] of the truth, there no longer remains a sacrifice for sins,
27 but a certain fearful expectation of judgment, and fiery indignation which will devour the adversaries.
28 Anyone who has rejected Moses' law dies without mercy on the testimony of two or three witnesses.
29 Of how much worse punishment, do you suppose, will he be thought worthy who has trampled the Son of God underfoot, counted the blood of the covenant
by which he was sanctified a common thing, and insulted the Spirit of grace?
30 For we know Him who said, "Vengeance is Mine, I will repay," says the Lord. And again, "The Lord will judge His people."
31 It is a fearful thing to fall into the hands of the living God.
32 But recall the former days in which, after you were illuminated, you endured a great struggle with sufferings:
33 partly while you were made a spectacle both by reproaches and tribulations, and partly while you became companions of those who were so treated;
34 for you had compassion on me in my chains, and joyfully accepted the plundering of your goods, knowing that you have a better and an enduring possession for yourselves in heaven.
35 Therefore do not cast away your confidence, which has great reward.
36 For you have need of endurance, so that after you have done the will of God,
you may receive the promise:
37 "For yet a little while, And He who is coming will come and will not tarry.
38 Now the just shall live by faith; But
if anyone draws back, My soul has no pleasure in him."
39 But
we are not of those who draw back to perdition, but of those
who believe to the saving of the soul.
Hebrews 10:26-39
This is not the description of a people who simply have "
head knowledge", but rather this describes people who have been cleansed by the blood of Jesus and have the Spirit of Grace, since they are being warned not to count the blood of the covenant,
by which they were sanctified "a common thing" which is insulting the Spirit of Grace.
Peter says it this way and uses the same Greek word in the phrase "knowledge [1922] of the Lord Jesus Christ"
20 For if, after
they have escaped the pollutions of the world through the knowledge [1922] of the Lord and Savior Jesus Christ, they are again entangled in them and overcome, the latter end is worse for them than the beginning.
21 For it would have been better for them not
to have known the way of righteousness, than having known it, to turn from the holy commandment delivered to them.
22 But it has happened to them according to the true proverb: "A dog returns to his own vomit," and, "a sow, having washed, to her wallowing in the mire."
2 Peter 2:20-22
It is not by
"head knowledge" were are sanctified, and it is not by
"head knowledge" we escape the pollutions of the world.
It's certainly not by "head knowledge" that we
have known [intimately experienced] the way of righteousness...
JLB