First you must alway remember to quote scripture in context. This scripture is talking about the religious people in the last days here on earth. It speaks of people who appear to be Christians but continue to live an unGodly lifestyle.
2 Timothy 3:1-9
1 But know this, that in the last days perilous times will come: 2 For men will be lovers of themselves, lovers of money, boasters, proud, blasphemers, disobedient to parents, unthankful, unholy, 3 unloving, unforgiving, slanderers, without self-control, brutal, despisers of good, 4 traitors, headstrong, haughty, lovers of pleasure rather than lovers of God, 5 having a form of godliness but denying its power. And from such people turn away! 6 For of this sort are those who creep into households and make captives of gullible women loaded down with sins, led away by various lusts, 7 always learning and never able to come to the knowledge of the truth. 8 Now as Jannes and Jambres resisted Moses, so do these also resist the truth: men of corrupt minds, disapproved concerning the faith; 9 but they will progress no further, for their folly will be manifest to all, as theirs also was.
If 2 Timothy 3:7, I'm guessing it refers to a kind of "tunnel vision" i.e. people are always wanting to know or understand but can't accept what is right before them.
Ch 3: In the last days people will be proud, arrogant, abusive and treacherous, lovers of pleasure rather than lovers of God. "(5) Avoid such people. (6)For among them are those who creep into households and capture weak women, burdened with sins and led astray by various passions, (7) always learning and never able to arrive at a knowledge of the truth."
Gullible women loaded down with sins and led away by various lust, indicating their vulnerability to the false teachers. These women continually sought, greater knowledge, but the very falseness of their teaching left them in ignorance of the truth
"Ever learning, and never able to come to the knowledge of the truth." - 2 Timothy 3:7 - To me, it's talking about people who learn and study the things of the physical world without ever learning about the nature of the spiritual world.
7 Ever learning , and never able to come to the knowledge of the truth. ----------/ You hear it all the time, people claiming they are Christian yet are not at all like Christ. They may quote the bible but they do not have it internalized, they have no real understanding of Christ and the word.
It's best to read all of 2 Timothy chapter 3. In the first few verses it talks about the attitudes of many people. In verses 2-5 it says, "For men will be lovers of themselves...having no natural affection, not open to any agreement, slanderers, without self-control, fierce... having a form of godly devotion but proving false to its power; and from these turn away."
If you'll notice in this part of the chapter is says that these people were "having a form of godly devotion but proving false to its power." (2 Timothy 3:5) It's these people that verse 7 is discussing when it says, that they are "always learning and yet never able to come to an accurate knowledge of truth."
However, this should not discourage us from reading the Bible and learning about God. In that same chapter, at 2 Timothy 3:16,17 it says, "All Scripture is inspired of God and beneficial for teaching, for reproving, for setting things straight, for disciplining in righteousness, that the man of God may be fully competent, completely equipped for every good work." So you see, we should continue to learn about God and try our best to live in a way that is pleasing to him.
A very good question. The preceding verse (2 Tim 3:5). Reveals that these corrupt men come from among persons "having a form of godly devotion but proving false to its power." They are those described by apostle Paul as "false apostles, deceitful workers, transforming themselves into apostles of Christ." In one translation. 2 Cor. 11:13-15 "God never sent those men at all; they are "phonies" who have fooled you into thinking they are Christ's apostles. Yet I am not surprised! Satan can change himself into an angel of light, so it is no wonder his servants can do it to, and seem like godly ministers. In the end they will get every bit of punishment their wicked deeds deserve." (Living Bible). In the first century C.E. these false teachers threatened the Christian standing of the Corinthian congregation, prompting the apostle Paul to write; "But I am frightened, fearing that in some way you will be led away from your pure and simple devotion to our Lord, just as Eve was deceived by Satan in the Garden of Eden. You seem so gullible; you believe whatever anyone tells you even if he is preaching about another Jesus than the one we preach. or a different spirit than the Holy Spirit you received, or shows you a different way to be saved. You swallow it all." 2 Cor 11:3-4 (Living Bible). Not only did such men seek to corrupt Christians by means of false teaching, but also tried to involve others in immoral conduct. As the disciple Jude noted: Jude 4 "I say this because some godless teachers have wormed their way in among you, saying that after we become Christians we can do just as we like without fear of God's punishment. The fate of such people was written long ago, for they have turned against our only Master and Lord , Jesus Christ."(Living Bible)
"To know" means that you have learned it and incorporated it into your life. If you just learned it, you could repeat it as often as you want, and it would still be empty words because you did not know them.