Patripassionism is a theological error dealing with the Godhead which states that the Father became incarnate, was born, suffered, and died on the cross, hence, the Father's (patri) passion (suffer) on the cross.
This is an error because we know that Jesus spoke to the person of the Father and that it was Jesus who went to the cross. If the Father and Son are the same person, that how is it possible for the Father and Son to speak to one another and have separate wills? It is not. Therefore, the doctrine of patripassionism is incorrect and heretical.