Originally INT was for attack magic, and MND was for healing magic. We had the Cleric Stance button on healers so they could swap their MND to become INT, so that they could cast potent attacks.

So basically INT is a stat that represents the ability to aetherically tear down, destroy, dissolve, dissipate, or disassemble another being. MND is the stat the focuses on building up, reinforcing, healing, mending, or otherwise reversing or preventing harm.

Nowdays there's no difference gameplay wise. They might as well trim out both stats and replace them with MP - Magical Potency.