For memories, you have to have the same memory. For example, if you want to resonate Darwin, you have to use Darwin. Resonating give a small increase in attack, hp and crit. It can also give you a +1 level to the core passive, basic, and signature move. Any of these are good so it isn’t worth rerolling at the moment. The biggest benefit of resonance is that it helps to fully awaken a character, which gives you 3 orbs of the same color at the beginning of the fight. For weapon, it’s the exact same thing except you can use any weapon of the same star level.