"And he began to speak boldly in the synagogue: whom when Aquila and Priscilla had heard, they took him unto them, and expounded unto him the way of God more perfectly." (Acts 18:26)
The man referred to in this verse—Apollos—was certainly no novice or first-year Bible student. His resume, according to verses twenty-four and twenty-five, would have read something like this: "Mighty in the Scriptures; eloquent and fervent in speech; diligent in the things of the Lord." Verse twenty-five ends by saying, however, that there was a gap in his knowledge. He knew only the baptism of John. By this, I take it that his conception of baptism did not go beyond John's physical to the Holy Spirit's (Luke 3:16), a serious deficiency in any believer's Bible knowledge.
Now Apollos could have reasoned, "Hey, I've got a great ministry going here. I'm being used, aren't I? What could this couple, who're just tent makers, add to me?" To his credit, however, he did not reason that way; and because he was willing to allow Aquila and Priscilla to expound the Word of God "more perfectly" to them, we read in verses twenty-seven and twenty-eight that he was able to be even greater help to the brethren and make an even more convincing argument for the Deity of Jesus Christ from the Scriptures.
If this Bible teacher and great orator needed instruction and correction, wouldn't it be safe to say our own Bible knowledge is always going to need some perfecting? The catch, however, is whether or not we are willing to allow God to use whomever He chooses to do the teaching and/or correcting. Pastors, elders, and teachers, to be sure; but we must never forget to be on the look out for that humble man or woman—whatever their occupation or station in life—who knows God, lives in His Word, and therefore, may be well qualified to perfect what is lacking in our Christian experience.
The word, "teachableness" has lost favor in today's vocabulary, and, sadly, so has the virtue itself. But you and I should constantly be nurturing this grace in our lives, since it is obvious that our usefulness to God will always be in direct proportion to how teachable we are.
He who will not learn from the unlikely is unlikely to learn at all.