We might think that truth will be self-evident and will protect itself.  In one way, that is so: God’s truth can never change.  On the other hand, our understanding of truth and how we respond to it can change.  The world, our own fleshly appetites and the devil’s scheming are constantly seeking to distort everybody’s perception of the truth.  Wickedness suppresses truth (Romans 1:18).  So, when a teacher does not hold fast to the truth, the effect will corrupt many people.  Jesus said that false teachers will deceive even those who think they are spiritually secure (Matthew 24:24).

Paul urged Timothy not to stray from what he had been taught.  The best way to do that was for Timothy to keep reminding himself of what Paul had said, treasure it as the Word of God, believe it and accept it as a love-filled gift from Jesus.  That task would require personal discipline to reject all other teachings which were different from what Paul taught (Galatians 1:6-9), and a dependence on the Holy Spirit (the Spirit of Truth – John 16:13) to keep living and teaching the truth.  

Timothy, like Titus and every believer, was a trustee of the truth (Titus 1:9).  Jesus had taught Paul, and Paul taught Timothy: now Timothy must not deviate from what Paul taught or else he could not bring the truth of Jesus to the churches (2 Timothy 4:3).  Thousands of false doctrines have always sprung up, and some have even become culturally acceptable in churches.  But when a church diverts from the apostles' teaching, it becomes sterile and unable to reproduce spiritually.  It is no longer a gospel church.  Although its participants may be happy in their self-regulated club, over a period of time the church loses its ability to proclaim the saving grace of Christ.

We also need to guard the truth.  Straying from believing and acting upon the apostles' doctrine can never bring God’s peaceful presence (Philippians 4:9); it is apostasy.  Abandoning the truth has been the downfall of many individuals, churches and ministries.  Yes, find new ways of presenting the truth, but never try to change the truth itself.  Ask yourself, ‘Have I strayed from the teaching of the apostles?’  How you deal with the answer may protect you and those you influence far more than you realise.