2 Timothy 2:15 Study to shew thyself approved unto God, a workman that needeth not to be ashamed, rightly dividing the word of truth.
I'm all for reading books, commentaries and sermon notes.
However, if we're not careful, we can end up only studying theological SYSTEMS found inside books written by men. If we were to attend one of these author's conferences or colleges in agreement to what they've written, we would be approved by their staff, faculty, pastors and leaders.
We should much rather consider being approved by God by studying His inspired scriptures. Studying God's word will develop us into unashamed workmen for Him.
Our study doesn't need the praise of men, it needs the approval of God.
To make your calling and election sure, study God's WORD, not man's WAY!
2 Peter 1:10 Wherefore the rather, brethren, give diligence to make your calling and election sure: for if ye do these things, ye shall never fall: