MacRae is a strong Scotsman specializing in unarmed combat. He helps the Blades defend themselves, going so far as to teach them hand-to-hand combat techniques. This way, they might have a better chance against the deathclaws and the Regulators.
MacRae is a Scotsman in the same way Patrick is a Celt. They are most likely descendent from a family trying to keep its heritage alive.
In return for aiding the Blades in ridding themselves of the Regulators, MacRae promises to train the Vault Dweller in unarmed combat. The code does not operate as it was supposed to however, and gives no bonus whatsoever, instead of the +1 melee damage and +5% Damage Resistance it was intended to.
The codes to give Damage Resistance bonuses to the player were fixed for Fallout 2, with the Dermal and Phoenix series of implants; the first 'quest' interaction after the Temple of Trials (by proximity to the starting point) is a fellow tribe member, Lucas, offering to give combat training, and there were a total of four such opportunities to learn Unarmed skill for 'free' in Fallout 2, so the developers may have been eager to redress this mistake in the first game.