Justice wasn't upholding some lofty, idealistic laws, it was doing what was right. It was this decision that caused Tyrael to learn the true meaning of justice. Tyrael would have to choose between following the law and letting the exiled leaders of Hell destroy mankind or intervening to help save humanity and turning his back on the one central ideal he held most dear. Eventually Tyrael would come to face one of the most difficult decisions of his existence when humanity was endangered by the release of the Prime Evils onto Sanctuary. Tyrael would spend much of his time observing humanity, but direct interaction was forbidden by the laws of Heaven. While at first many angels saw humanity as an abomination, Tyrael saw the potential for good that resided within this new race. Humans were the spawn of rogue angels and demons who had become weary of the endless Eternal Conflict that consumed all of the focus of both Heaven and Hell. This view of Creation was shattered once he encountered the denizens of Sanctuary, humans. For countless eons Tyrael thought the only principles of justice were the laws of the High Heavens.
He has fought against the forces of Hell since time immemorial. As Archangel, Angel and Aspect of Justice, leader of the Heavenly Host and a member of the Angiris Council, Tyrael was born from one of the virtues of the great titan Anu at the beginning of time.