Proverbs 22:21

That I might make thee know the certainty of the words of truth; that thou mightest answer the words of truth to them that send unto thee?

Wise counsel and knowledge make the certainty of true words known and fit a person to give an answer to those who send to him and seek an account from him.
This certainty is given in order that trust may rest in the Lord.
Its reliable source is the Lord's own teaching, which imparts sound counsel instead of polluted or false ideas.
In its immediate setting this dependable divine instruction stands together with commands to protect the poor and to shun corrupting influences.

True words are to be kept within and held ready for clear witness to others.
That certainty comes through diligently searching Scripture point by point and receiving instruction and understanding from God.
After the disappointment such searching brought truth into view and equipped its seekers to proclaim it to the world.
That study made the prophecies plain and equipped believers to proclaim the messages with assurance and in unity.