Isaac, whose name means laughter, is the joy born late in the awakened person, the son of the higher faculty who must be laid upon the altar of transformation. His question about the lamb is the inner asking of the newly risen soul that sees the elements of sacrifice prepared but does not yet understand what must be given. The fire is the purifying spiritual energy, the burning force that consumes the lower nature, and the wood is the physical frame laid ready to bear that flame. Abraham, the father, is the exalted will that has heard the higher command and moves toward it without wavering. The lamb sought is the innocent lower self, the part that will be offered up so the divine may be released, and the son does not yet see that the offering asked is bound up with himself.
What unfolds inside a person is the moment the awakened joy confronts the fire prepared for it and begins to sense that its own lower nature is the thing to be surrendered.
Isaac: the joy born late in the person, the son laid on the altar of transformation
Fire: the purifying spiritual energy that consumes the lower nature
Wood: the physical frame laid ready to bear the burning force
Lamb: the innocent lower self offered up so the higher nature may be released