The relationship between Saul, Jonathan and David is very complex. It occurred to me that it is played out via their weapons of choice.
Saul's weapon is the Spear.
Jonathan's weapon is the Bow and Arrow.
David's weapon is the Slingshot and Stone.
All three of these weapons are the same in that all of them take flight in order to be effective. They are not like a sword, where one simply thrusts the sword through a person, or hacks them with it.
But Jonathan's weapon is most similar to David's weapon because both of their weapons require something else to launch it. Jonathan's bow launches his arrow and David's slingshot launches his stone, but Saul's hand is what throws the spear. Thus, Saul is different from the two of them. In the end, Jonathan and David are most similar to one another.
My student expanded upon this idea. He said that he thought that the Bow and Arrow and the Spear are similar, because an Arrow is like a Spear, just smaller.
I ran with his idea to create this:
Jonathan's weapon shows the tension and inner struggle of his character. On the one hand, the bow and arrow is similar to Saul (the arrow has the same pointy tip as the spear). On the other hand, the bow and arrow is an implement being launched by another implement, similar to David. Jonathan is similar to both and has loyalties to both- hence his inner struggle, conflict and tension.