I'm planning to build a countertop for the kitchen out of glued 1 x 1 pieces of pine. I have glued the pieces together and it looks good, but after working with it for a while, I have realized that it is softer than I initially thought, so I was wondering if there is any treatment for the surface to make it stronger? It feels like if there is a heavy object falling on it, will make a "beautiful" dent in it. I can see videos with people filling gaps with epoxy and that epoxy looks strong, but is epoxy an alternative for this? Can it be applied to the surface only? What other solutions would you recommend for this?
The comments have a lot of good discussion about wood choice, but to directly answer your question, yes. You can use epoxy to make a surface harder. However, you need to be careful about your choice of epoxy.
Normal hardware store epoxy is designed for repair work, i.e. bonding two parts together. To do this effectively it needs to be quite thick. This will prevent it from "soaking into" the surface you're treating. Instead, you should use a "penetrating epoxy sealer". This type of epoxy is much thinner and will "penetrate" deeper into the wood you're treating.
Epoxy (along with most wood glues and finishes) is generally food safe once it has fully cured.
I would recommend doing a test on a scrap to see how the epoxy will effect your finishing.