Every single person on the quest to the west was brought for a reason.
Ferro - demon blood and can wield the seed
Ninefingers - to summon and talk to the spirit at the location of the seed
Longfoot - to guide them (and perhaps even boast here or there)
Quay - apprentice in learning
But why not Jezal? It was never revealed. But Bayaz didnt assist in the tournament, steal Jezal from going to Angland, and whisk him away on a grand adventure for no reason. So I have a prediction. I feel as though with the succession on the line and all the cut-throat politics that it will bring, Bayaz may stay to influence the selection of a new ruler. Perhaps Jezal is the king the Union may need. He i