Michael had his reason for matching Luis with Silvia, he had discovered that Luis mostly fought with his weapons and hardly used his fists and legs.
He wanted to show him that despite being an Angel he was desperately lacking when it came to physical combat, although weapons were made to help humans fight, there were certain situations where one would no longer have his weapon on the battlefield and he would have to resort to using his fists and legs, yes he had done well in bringing Michael down during the time he challenged them but that was because Michael didn't go all out on him.
He wanted to show Luis that he was lacking in physical combat and the best person to help him do that was the wonder warrior, who had received a series of combat lessons and training even as a little child.
Because of his inexperience when it came to physical combat Luis had been the first to lose out on the spar.
