But, of course, only up to and not including the slaughter. In more mystical circles the sacrifice is deemed to have actually occurred on the heavenly mirrored altar. We and all Avraham's progeny are the beneficiaries of this deed. We continually hearken back to that act because of the merit accrued. The second way to go with this idea is more prosaic.
Testing is a method for strengthening things.
We harden and refine products through a process of pushing a material's ability to withstand the heat or pressure. Sometimes we hit a pot not to show its worth but to demonstrate its strength. And sometimes we smack flax to improve the quality. While other times we pile on the load because we want to share the world's burdens. Hashem did all three with Avraham.