Paul is instructing Timothy to not waste time arguing about godless ideas but to spend time learning and understanding the truth. It is likened to spiritual fitness. I had been a competitive bodybuilder, ran a marathon, played brutal flag football and been on a crewing team to mention a few. There was a lot of effort and training put into my preparation for those events. Verse 4:8 tells us that while physical training has value, spiritual training has even greater value. To apply the same diligence and determination to know how to compete in such events would be well spent in spiritual training in preparation for times when I need to know the truth and help another who might be confused. While my pursuit of physical training had it's rewards here and now, being trained spiritually has it's rewards here and now as well as in life after this life.
Paul teaches Timothy to work hard, know the truth of the Word of God and help others walk in that truth. We would do well to do the same. He also encourages Timothy to not let age be an issue and to be confident. His instruction continues with what we might take on for ourselves in the latter part of verse 4:12; (The Book translation) "Be an example to all believers in what you teach, in the way you live, in your love, your faith, and your purity." A great mirror to view ourselves in.
Lastly his instruction is to use gifts, pay strict attention to what we do, and stay true to what is right.
Do not take such things lightly, remember the battle is spiritual and we need to prepare with knowledge and understanding. Keep on studying, you are all doing great.