For context, the canons are divided into five "heads" with a number of articles (and rejections of errors) under each heading. Here are the five heads:
FIRST HEAD OF DOCTRINE. DIVINE ELECTION AND REPROBATION
SECOND HEAD OF DOCTRINE.THE DEATH OF CHRIST, AND THE REDEMPTION OF MEN THEREBY
THIRD AND FOURTH HEADS OF DOCTRINE. THE CORRUPTION OF MAN, HIS CONVERSION TO GOD, AND THE MANNER THEREOF
FIFTH HEAD OF DOCTRINE. THE PERSEVERANCE OF THE SAINTS
Now continuing on with the first head, we are at article 3:
FIRST HEAD: ARTICLE 3. And that men may be brought to believe, God mercifully sends the messengers of these most joyful tiding to whom He will and at what time He pleases; by whose ministry men are called to repentance and faith in Christ crucified. "How, then, can they call on the one they have not believed in? And how can they believe in the one of whom they have not heard? And how can they hear without someone preaching to them? And how can they preach unless they are sent?" (Rom 10:14-15).
God, having chosen some undeserving persons out of all the undeserving persons in the world and of all time to have eternal life, provides the means to obtain eternal life. How is it that sinful man can or will believe the good news that Jesus came to save sinners?
The canons assert here that God is merciful such that He sends messengers carrying good news (Romans 10:14-15 as is noted). And further, He sends this joyful good news when and to whom He pleases. After all, He is sovereign over all. Stories abound of conversions where men testify how that someone sort of mysteriously came into their lives and shared the grace, the good news of Jesus with them.
These "messengers" with the good news...who are these messengers? Preachers, teachers, firemen, students and the like. Businessmen, housewives, store owners, managers, etc. In other words, all of us who name the name of Christ.
Article 3 simply tells us that God saves His people by means of other of His people sharing that good news that Jesus saves sinners. SDG!