John 5:36
But the testimony that I have is greater than that of John. For the works that the Father has given me to accomplish, the very works that I am doing, bear witness about me that the Father has sent me.

Hebrews 12:1
Jesus, Founder and Perfecter of Our Faith
Therefore, since we are surrounded by so great a cloud of witnesses, let us also lay aside every weight, and sin which clings so closely, and let us run with endurance the race that is set before us,

Living a life of faith is our greatest witness.

Preach the gospel wherever you go, and if you must use words.

2 Timothy 2:15 Do your best to present yourself to God as one approved, a worker who has no need to be ashamed, rightly handling the word of truth.

If we have the Holy Spirit to lead us in all truth, why do we need pastors and teachers?

Ephesians 4:10-12 English Standard Version

¹⁰ He who descended is the one who also ascended far above all the heavens, that he might fill all things. ¹¹ And he gave the apostles, the prophets, the evangelists, the shepherds and teachers, ¹² to equip the saints for the work of ministry, for building up the body of Christ,

Equipping the saints is a process that takes time. First we must see to the issues associated with calling the lost and seeing to their training in the word of truth.

There is a transitional period where the renewal of the mind unlearns worldly ways and aligns understanding and belief measured against the whole counsel of God.

Isaiah 28:17 And I will make justice the line, and righteousness the plumb line; 

Think of the plumb line as the vertical application of truth related to the base, that is square and true, not skewed. It must not be moved by every wind of doctrine.

Ephesians 4:14 so that we may no longer be children, tossed to and fro by the waves and carried about by every wind of doctrine, by human cunning, by craftiness in deceitful schemes.

Amos 7:7 This is what he showed me: behold, the Lord was standing beside a wall built with a plumb line, with a plumb line in his hand.

What is built upon the Cornerstone must meet His exacting standards.

Teachers are to keep measurements of their teaching to the rightness of the plumb line.

Titus 1:9 He must hold firm to the trustworthy word as taught, so that he may be able to give instruction in sound doctrine and also to rebuke those who contradict it.