"And he [David] took his staff in his hand, and chose him five smooth stones out of the brook, and put them in a shepherd's bag which he had, even in a scrip; and his sling was in his hand: and he drew near to the Philistine." (1 Samuel 17:40)
Why did young David choose smooth stones for his sling? From minimal research I found out that smooth stones sail through the air faster and straighter than rough, jagged ones, which tend to curve unpredictably. How do rough stones become smooth ones? Geologically speaking, this happens through a process called "tumbling," which is "usually accomplished by transportation of the stone by water and contact with other rocks." Of course, Job knew this, thousands of years earlier (Job 14:19a).
If I might, I'd like to take the liberty of drawing an analogy here. If God wanted, as David did, to defeat His enemy using you and me "as lively stones" (1 Pet. 2:5), would He want us to be smooth or jagged, do you think? If the former, then that will require two things: water (Eph. 5:26), and "contact with other rocks." And not necessarily the gentle tapping kind, either. In fact, I would imagine the rougher the encounter, the quicker the smoothing process.
Maybe you're like me. There are people, even other believers, who just "rub you the wrong way?" As someone has pointed out, only hard things can wear out hard things. Maybe we should look at these people in a whole different way. Instead of seeing them as irritating nuisances sent by Satan to sabotage our Christian life, maybe we should consider them as possible refining tools God is using to make us more proficient instruments of battle in the good fight of faith, helping us to fly farther, faster, and more accurately.
To quote John the Baptist’s first sermon, “…the rough ways shall be made smooth” (Luke 3:4); and my prayer is that the Lord will make my own rough edges smooth. It may be painful, but by His grace, I want to be a "smooth stone" in the hand of God.