In an article about mythology, I wrote: "As a child grows into a man, the soul is gripped ever tighter in the mistaken belief of separateness from all other humans and from God. This belief in individuality manifests itself in dominance of the ego. Our earthly ego is the dragon blocking the gateway from the material world back to the spirit world." Link.
Thus, the inner meaning to symbolically slaying the dragon is the destruction of our own earthly ego. This monstrous ego blocks the path back to God. Jesus doesn't talk about dragons or monsters but he does say we must become as children again to enter the kingdom of God. Newborn children are trusting, innocent beings lacking an ego.
One hears Christian sermons on the subject of being broken as was Jesus at Golgotha. See sample. In the ritual which is the Roman Catholic mass, the priest relates the words of Jesus referring to the bread as his body and instructing that the bread is to be broken then eaten in remembrance of him.
Jesus said, the stone which the builders rejected became the cornerstone. “He who falls on this stone will be broken to pieces, but on whoever it falls it will scatter him like dust." Matthew 21:44. At first read, neither alternative offered by Jesus looks promising, i.e., being broken or being scattered. No other alternative is mentioned in the parable. But, perhaps, this is the ultimate fate of us all. "Man you are dust and to dust you shall return." Option 2 is inevitable. We all must return to dust. But option 1 involves action on the part of the individual. If we fall on "the cornerstone". "The cornerstone" of which Jesus speaks in Matthew 21 is the teaching of Jesus Christ, the "Word" if you will. Fall upon the Word and your ego shall be broken (the dragon slain) opening up the path back to the kingdom of God.