Ver. 20. _Self-conscious Truth._--1. The choicest servants of Christ may be looked upon as liars and unworthy to be trusted, even by those to whom they are sent, and yet they must not give over to preach as knowing that the Word spoken by them doth still get credit from some, and will beget trust to itself from others, and for the rest it will seal up their condemnation and make them inexcusable. 2. It is not unlawful for Christians to take an oath, providing it be with these conditions: (1) That the thing we swear be truth. (2) That there be weighty reasons for taking an oath. (3) That we swear only by the name of God, and not by the creatures, seeing none but God can bear witness to the secrets of the heart.--_Fergusson._ Vers. 21-24. _The Self-evidencing Proof of a Divinely commissioned Messenger._--1. Seen in disinterested labours and travels (vers. 21, 22). 2. Seen in a remarkable change of character and conduct (ver. 23). 3. Seen in that the glory of his work is ascribed to God (ver. 24). _Practical Proofs of Apostleship._ I. +Paul went from Jerusalem into Syria and Cilicia.+--1. Because he was ordained specially to be the apostle of the Gentiles. 2. Because Cilicia was his own country, and his love to his country was great. If any apostle above the rest be the pastor and universal bishop of the Church over the whole world, it is Paul and not Peter. II. +Paul was known to the Christian Jews only by hearsay,+ because it is the office of an apostle not to build on the foundation of another or to succeed any man in his labour, but to plant and found the Church of the New Testament. III. Seeing the intent of the devil and wicked men is to destroy the faith, +we must have a special care of our faith.+--1. We must look that our faith be a true faith. 2. We must keep and lock up our faith in some safe and sure place--in the storehouse or treasury of a good conscience. 3. Our care must be to increase in faith that our hearts may be rooted and grounded in the love of God. IV. +Our duty is to sanctify and glorify the name of God in every work of His.+--Neglect in glorifying and praising God is a great sin.--_Perkins._