The Vates, their name meaning approximately seer and prophet, were sacrificial priests and naturalists who knew a great deal about plants, herbs and heavenly bodies. They were not very different from the Druids and Bards.
If a Vates had a profession as a seer or as a soothsayer, he had to elevate his consciousness in a higher form. When he went into ecstasy, no comparison should be made with the Shamans of the Arctic peoples of Northern Europe and Asia. These priests, the Vates, were more interested in the will of God and sought to examine it in this way.
The Vates were also naturalists, but not out of scientific interest.
They examined the phenomena in the sky for proper preparations to perform the offerings. These were the most suitable times and so, for example, the new or the full moon were important times to be able to sacrifice. Offerings at the proper times involved much preparatory work, and several priests were in charge of this. The sacrifice was evidently a complicated affair.
It is generally accepted that the Gallic Vates heard the voice of God when in a trance and that their proclamation was clothed in poetic language.
To the Celts, the function of these inspired Vates was incredibly important.
Evidently, the Celts had an extensive priestly class that divided their various activities into several functions. The Vates had a closed community and were also involved in genealogy and law, although ultimate jurisdiction rested with the king. In pre-Christian times, this is how the state of judges arose. The Vates dealt with the interpretation and they commented on the law. In the distant past, they prophesied about sacrifices and the flights of birds. In later times, they acted more as poets and makers of songs of mockery and praise, having a special magical effect on those to whom they sang. These activities are reminiscent of the activities of the Bards.
Their magic also extended to natural phenomena: they could lower or raise the water level in lakes and rivers and that naturally commanded a certain respect.
 Hans Gsänger, Irland. Insel des Abel. Die irischen Hochkreuze [Ireland. Isle of Abel. The Irish high crosses], Verlag Die Kommenden, 1969
 Jakob Streit, Sonne und Kreuz [Sun and Cross], Freies Geistesleben, Stuttgart 1977