You are asking about the familiar and beloved story of David and Goliath described in I Samuel 17:31-49. (I'm not going to transcribe the full text here.)
The essence of a metaphysical approach to the Bible is that it becomes the personal story of each individual who approaches it. The characters become ideas and attitudes in our own consciousness, and the unfolding drama depicts conflicts that each of us experiences in the course of moving forward toward full spiritual awareness and expression—that Christ consciousness that Jesus Christ teaches and demonstrates.
That Christ consciousness doesn't come upon us at first as a full-blown, adult teacher and demonstrator of spiritual truth. Its earliest expression may be as an apparently insignificant child—a simple spiritual clarity, easily dismissed by the more practical, experienced "grown-up" thoughts that have long maintained control of our consciousness, and thus of our lives. It often requires a state of absolute desperation—when we come up against an obstacle for which "knowing what we know" offers no solution—that we may become willing to hear what the small voice of the Christ child within has to say.
So it is here. The adults see Goliath as a huge, insurmountable obstacle against which they have no defense. Young David sees, with the simple clarity of childlike faith, that Goliath is not of God. Therefore, no matter how big or scary he might appear, he is only an illusion, and the question is clear: "Who is this uncircumcised Philistine, that he should defy the armies of the living God?" (I Sam. 17:26). (I find this a useful question in many circumstances!)
So metaphysically the importance of what happens is not that a brave little kid goes up against a mammoth bad guy and wins. The important thing is that David does not see a scary big dude. He sees an illusion that is not of God, and so has no reality in truth, and so is not to be feared. We see this in the fact that, while the adults try to cover the kid in armor to protect him, and provide weapons with which to do battle, David shrugs them off. The fear-based accoutrements of old consciousness will simply get in the way once we allow the tiny voice of spiritual truth to stand forth. All he needs is a stone—the word, the seed of spiritual truth—and a sling—a willingness to send that seed forth.
And it's true for all of us as we come up against apparent challenges in the course of any given day. No matter what it is that seems to be standing in our way, the clear perception of David—the voice of the Christ child within us—will always prevail: "You come to me with a sword and with a spear and with a javelin; but I come to you in the name of the Lord of hosts, the God of the armies of Israel. ... This day the Lord will deliver you into my hand." And so it is.