Paul addressing the people of Corinth said;
1 Corinthians 3:10 According to the grace of God which is given unto me, as a wise master builder, I have laid the foundation, and another buildeth thereon. But let every man take heed how he buildeth thereupon. 3:11 For other foundation can no man lay than that which is laid, which is Jesus Christ.
In the earlier verse, Paul had addressed them as "babe", people who were spiritual immature because among them was still found strife, hatred, envy, and division. Growing spiritually requires a gradual process of inner transformation from our carnal ideologies to a godly form of living, this godly virtue was what was lacking in the lives of the Corinthians and their response was still worldly. Among us are people who God has given the gift of prophecy, teaching, healing, discerning, etc. And this set them a little bit ahead of us in knowledge. It's true that the bible is the word we need to feed on to reach spiritual maturity, and also true that Jesus Christ had laid the foundation for us to build upon, but again, GOD had endowed some groups of people with gifts even in this era in order to guide us toward this maturity.
Religious teachers are people believed to have studied in depth and have had knowledge of the rhema of God's word. We have the logos and the rhema,
The logos is the general word of God that communicates his ability to do something or his general will on a matter while a rhema is the word the Holy Spirit quickens to a specific person for a specific situation.
We may study God's word and only have the logos without getting the rhema and this is the main reason why we need a teacher in order to grow spirituality. The people of Corinth still acted like babes who still held on to envy and malice because they had no rhema of what spiritual maturity entailed. They have heard the word, but at that time had no leader(spiritual teacher) to build on the word to which they've heard. Without the rhema, we still hold onto our philosophy about life, we may sometimes try to coin God's word to fit our daily life, thereby losing the whole essence of spiritual growth- which is to put away our past life, philosophy, and ideology and embrace the life of Christ.
Do not get me wrong, an individual can have both the logos and rhema of God's word if he dig deeper and seek God's wisdom to be able to interpret the logos, but we still need someone who's experience, gifted, and had been anointed by God to guide us through this pilgrim path, and a path to this spiritual growth. We are like babies still suckling on our mother's breast awaiting a period to be weaned. If our daily diet is nutritious, we may grow healthy and be able to eat solid food. Spiritual leaders or teachers are just like the parents whose breast we are suckling from to be mature enough to eat solid food.