I don’t know about this allegorical use of the five stones. I believe David knew that he only needed one stone, but that Goliath had four brothers, one for each of the remaining stones. Eh? This is an unwritten, but literal, practical application of the passage. David did not need to do the killing of the others. His pals did it.
If you read the Old Testament from a military point of view you can see that the Israelites were a bunch of fierce and tactically savvy warriors. They left little to chance and took advantage of technology, terrain, weather and even the season of the year and time of day to launch their offensives. They have forgotten nothing in 3000 years. Sadly, thousands may have to perish to reaffirm this fact.
Hmmm - no stone for Faith? Wasn’t that what gave David his triumph? Faith in the Lord.