The second letter to Timothy is the middle book of what is often called the pastoral letters. Paul is writing to his protege Timothy (and Titus, in the book bearing his name) about pastoral ministry in the places where they serve.
And I love what he drops into the end of 2 Timothy 3.
All Scripture is breathed out by God and profitable for teaching, for reproof, for correction, and for training in righteousness, that the man of God may be complete, equipped for every good work. (3.16-17)
Paul has reminded Timothy before to keep at the business of being in and teaching the Word of God (1 Timothy 2, 4, etc.). And here he reminds him of the why.
All Scripture is breathed out (inspired) by God. The words that I have on the page in front of me are the words of God to me. God spoke them through His people so that I could understand. Wow.
And they're good for me. They teach me. They reprove me. They correct me. They train me.
To what end? That I may be ready to do what God says is good to do.
This is why we must spend time in the Word. We must read it and study it and memorize it and hear it and live it. It's so good and so good for us.