Good resources help equip you for the work you are doing. But resources also help you discover your calling. The more you read and study, the more God reveals to you about His work and how He can use you in it.
Good reading material and references for your spiritual growth and development are well worth the investment of time and money it may cost. They can help you to understand more difficult passages of Scripture. They can help you to protect and defend the faith. They can help you to grow spiritually and become more effective in your witness for Christ.