Merriam-Webster:
"repent -
1 : to turn from sin and dedicate oneself to the amendment of one's life
2a: to feel regret or contrition
b: to change one's mind"

BDAG:
"repent/μετανοέω -
1 change one's mind
2 feel remorse, repent, be converted"

While the lexicons give many varied applications of the word in scripture, the idea of "to change one's mind" is what I found so soul shaking and disturbing in regard to one's theological beliefs. What happens when, after many years being invested in particular theological views on salvation and/or eschatology, you come to find out you were very wrong, but had earlier been so sure and convinced of your biblical stand? During your change of mind you can begin to question yourself, form doubts about your own ability to understand God's word to us, and then think, can I really know truth at all? That can be scary! I had put too much trust in Pastors and teachers, but I knew I'd have to answer for myself on the last day. I experienced this doubt and disturbance earlier in life so I know how very disturbing it can be.

In spite of being under much heresy from the pulpits, I did hear references and quotes from men out of the past: Spurgeon, Knox and Luther for example. I reasoned that if those men from the old Lutherans, Presybterians and Baptists were good enough to quote; maybe the confessions of those denominations out of the past would be a proper guide; they had stood the test of time. While admitting they are by humans and can contain errors, there should be a core system of faith expressed and I found it in the various old confessions coming out of the Protestant Reformation, plus learning the ancient Ecumenical Creeds as well. Add to this the commentaries and theological textbooks out of the past and that soon forced me into study of hermeneutics. I came to have a perspective strongly based on the following, very basic or simple keys:

"Thus saith the LORD, Stand ye in the ways, and see, and ask for the old paths, where is the good way, and walk therein, and ye shall find rest for your souls. But they said, We will not walk therein." (Jer 6:16 KJV)

"Beloved, being very eager to write to you of our common salvation, I found it necessary to write appealing to you to contend for the faith which was once for all delivered to the saints." (Jude 1:3 RSV)

"I have applied all this to myself and Apol′los for your benefit, brethren, that you may learn by us not to go beyond what is written, that none of you may be puffed up in favor of one against another." (1Cor 4:6 RSV)

Isn't our relationship to God Almighty important enough to study with diligence? I've been mocked for building a rather large Bible reference library; but do we mock those who spend hours in mundane hobbies like hunting, fishing, stamp collecting, etc? Purchasing books and having subscriptions to the various hobby magazines can take time and money as well, do we mock that? There is a line in Hosea 4:6 "My people are destroyed for lack of knowledge", and that should not be ignored! Even the elect's comfort and assurance in their salvation can be destroyed in the here and now, not their eternal salvation of course.

Not only is it important for myself personally, it is very important for when family come to me asking for biblical advice, helps in theology, etc. I'm going to answer on the last day for what I instruct them also.