I am going to suggest that the heart of a good teacher is pure and righteous, seeking after God and desiring God's best for all. This person would be a believer who knows the Bible and believes it is the Word of God. They are also led by the Spirit so they get revelation insight, just as the disciples did on the Emmaus Road.

Biblical examples of teachers with a righteous heart, yet still needing and receiving ever-increasing revelation

1. I would say that Paul the Apostle had a pure heart even when he was a Pharisee. He knew the Bible and was passionate to obey it and teach it as he understood it. He was out killing Christians because he believed this was the right thing scripturally to do. I do consider that to be a false belief. Even though his heart was pure his theology was un-enlightened and false, so he was half-cocked and not doing God a service because of his messed up theology. The thing he was missing was the spiritual insight that he ultimately experienced when God encountered him in a vision in Acts 9. Paul revised his message immediately and began preaching that Jesus was the Messiah and he no longer sought to kill Christians.
2. I was like Paul in that I graduated from college with a Bible knowledge and a passion to preach and teach the Word and serve people.It took me 10 years before I had my first significant divine encounter. I was awakened by a booming voice, which was God instructing me. That morning He taught me four keys so I could hear His voice daily through two-way journaling. Then my preaching and teaching became much richer, more pure, more spiritual and more helpful, and the fruits of the Spirit became much more evident in my life.
3. Apollos had a pure heart but an incomplete understanding of truth. So Aquila and Priscilla took him aside and taught him a more excellent way, and he became an anointed teacher, sharing a fuller truth (Acts 18:24-28).

The fruit of the Spirit is seen in the heart of a true teacher and this fruit guides their actions

• Love, joy, peace, patience, kindness, goodness, faithfulness, gentleness, self-control; against such things there is no law. Now those who belong to Christ Jesus have crucified the flesh with its passions and desires. If we live by the Spirit, let us also walk by the Spirit. (Gal. 5:22-25)

• We don't need to reject, condemn, attack and call people heretics when they disagree with us. We choose blessing rather than cursing (Jas. 3:10). We respect those who disagree without becoming disagreeable. By choosing this, we obey Christ’s command to show honor (1 Pet. 2:17; 3:9), and prove to the world we are His children in that we love one another (Jn. 13:35). Maintaining honor and love are some of the weightier issues Jesus spoke of in Matthew 23:23 and Luke 11:42.

• We believe we can learn from anyone, including non-Christians. (For example, some believe, “You can’t learn anything from a New Ager.”) God granted revelation to Pharaoh, an evil king (Gen. 41) as well as to Belshazzar (Dan. 5). God gave insight to Jethro, Moses’ father-in-law, as to how to govern (Ex. 18). Everyone can receive God’s revelation. Therefore we can learn from all.

• We do not live in reaction to error. Some suggest we should live in reaction to the New Age, making sure we don’t do anything similar to what they do. The Bible never instructs us to live in reaction to error. We are to explore truth and live in the truth. We do not care if every cult group or no cult group believes things similar to what we believe. We believe what the Bible and the Spirit instruct us to believe, period!
   
• We believe it takes the Spirit to help us truly understand the Bible. We believe the Bible is the inerrant, authoritative, divinely-inspired Word of God (2 Tim. 3:16). Even as Jesus "opened the Scriptures" to the disciples on the Emmaus Road (Lk. 24:32, 45), so today, we need the Holy Spirit to assist us by opening the Scriptures to our understanding (Prov. 3:5). We “reason together with God” (Isa. 1:18) rather than reasoning on our own. We ask God for wisdom and tune to the river of the Holy Spirit Who flows within. This results in insight, illumination and revelation.  

The Bible likens the Christian life to a highway that we walk on

• The highway of the upright is to depart from evil; He who watches his way preserves his life. (Prov. 16:17) 
• The way of the lazy is like a hedge of thorns, But the path of the upright is a highway. (Prov. 15:19) 
• A highway will be there, a roadway, And it will be called the Highway of Holiness. The unclean will not travel on it. (Isa. 35:8)
• For My people have forgotten Me, They burn incense to worthless gods And they have stumbled from their ways, From the ancient paths, To walk in bypaths, Not on a highway. (Jer. 18:15)

Other Scriptures state that as we follow the path of the Spirit we gain more and more enlightenment and our teaching becomes more anointed and more powerful. To be an anointed teacher requires meekness, a willingness to learn, grow and change, and the ability to hear God’s voice and be obedient to what He is speaking (Jn. 10:27).

This short blog, "Stop, Focus, Ask", gives great guidance from Jesus on how we get increased light and understanding. Here is another blog which shows how we meditate on Scripture to get revelation.

Journaling application questions

1. Lord, what would You speak to me concerning having heart revelation to couple with biblical understanding?

2. Lord, what would You speak concerning my walking on Your Highway of Holiness?

It’s Not Heresy! It’s Enlightenment! (Part 4 of unfolding series, with the following blogs being posted over the next few weeks)

1. What Is a Heretic? Have I Been One? Who Defines Misinformation?
2. Shall We Remove the Words "Heretic" and "Heresy"?
3. What Is the Key Trait of a False Teacher?
4. What Is the Key Trait of a True Teacher?
5. God’s Highway of Holiness is SAFE
6. Roadblocks Removed on His Highway of Holiness
7. As I Travel God’s Highway, Revelation Shines Ever More Brightly
8. A New Day Dawns as the Morning Star ARISES in Our Hearts
9. Using e-Sword to Explore the Words "Heretic" and "Heresy"