Back in the old days when I was young, boys carried pocketknives everywhere—especially to school. Of course, we showed them off during recess and we whittled, not so much to make things but to prove whose knife was the sharpest. So, I learned to sharpen knives. And then Dad taught me to sharpen axes and I learned to take pride that my mower blades were as sharp as anyone's pocketknife. The mower cuts better and easier for a smoother lawn.
After I left full time preaching, I often preached by appointment in small churches and these were usually too far away to return home for lunch. Of course, someone would take me (or us) in for lunch. As a way to show gratitude, I would offer to sharpen their kitchen knives. I have been amazed to find that few know how to sharpen. I still recall one sister asking me not to get them too sharp so she would not cut herself. No amount of discussion or logic would convince her that a dull knife was more dangerous and more likely to result in serious cuts. But, it is true, one pushes harder to cut with a dull knife and it is more likely to slip and the force of the push will result in a more serious cut. A sharp knife would have cut the object more easily and resulted in no accident at all.
Dull knives are a danger in the church. Most of the trouble I have witnessed in 50 years has been caused by people of dull understanding but a sharp sense of the value of their opinion. They wield them wildly, slashing the air all about, certain that because they have not changed their minds in years, it must be truth. They bruise the innocent, slash the sensitive, kill the ignorant seekers.
But, should you attempt to sharpen their knowledge and understanding with sound scripture and unassailable logic, they will either go away in a huff or grudgingly concede, but spout that same dull basic or even erroneous point the next time that subject comes up. They can be sharpened no more than the edge of a two by four.
One's knowledge, understanding and abilities are not sharpened alone in the study. They are brought to a smooth and "sharp as a two-edged sword" edge by discussions with another of a different, even opposing viewpoint (sometimes, even sharp discussions). To become sharp, one must listen, then think, then give answer, listen, then think. If both are honest, one will change or both will. The truth may be that neither is wholly right but you are both sharpened by the discussion.
Think seriously: When did you last have an argument about the Word? An honest toward God argument determined to win and show the other the truth, yet also willing to listen. It likely has been too long and you have become dull in an age where no one wants to argue for anything.
The last step of sharpening a knife is to put it to the steel to true the edges. In fact, many times, this is all a knife needs as the edges were bent aside by being used. Thus, the chefs on a cooking show are often seen whetting their knives on a steel.
So, also do you. Learn something. Form an opinion. Go out to your friends and brothers and test it against the steel of other views. GROW sharper.
"Iron sharpens iron, and one man sharpens another. " (Prov 27:17).