The first of these instructions is found in 1 Tim. 1:3, which says to Timothy, . . . that thou might charge some that they teach no other doctrine. Timothy's job as a young preacher was to charge others to teach no other doctrine except that which was taught by Paul himself.
Why should Timothy teach only the doctrine that Paul taught? It is because Paul is an apostle of Jesus Christ by the commandment of God our Savior (verse 1). Being an apostle "out of due season," Paul had to continually vindicate his apostleship. As he did that, he was faithful to his cause as an apostle. He died in Christ so that he might live in Christ.
Ga 2:20 I am crucified with Christ: nevertheless I live; yet not I, but Christ liveth in me: and the life which I now live in the flesh I live by the faith of the Son of God, who loved me, and gave himself for me.
Timothy was to learn the same lesson that Paul learned: that Christ is all that is important. The world must pass away, but Christ must be taught. Man's wisdom is temporary and insufficient, but God's wisdom is powerful and sufficient for every purpose of reason.
All scripture is given by inspiration of God (2 Tim. 3:16), and all scripture is in unity in relation to the doctrines that it teaches. The writings of Paul which the Holy Spirit gave to him are all consistent in their teachings; and Timothy, being taught the scriptures from his youth, knew that Paul's doctrine was consistent with every scripture that Timothy knew.
Today many people are wanting us to listen to new revelations from God, but the only true revelation from God in written form is his completed and perfect word, the 66 books of the Bible.
In order to charge others, Timothy needed to study the word of God so that he could handle it appropriately (2 Tim. 2:15).
May we also study the scriptures so that we may instruct others to teach no other doctrine than that which is written in the scriptures.