Like Michael Baius, who was his senior colleague, Hessels preferred drawing his theology from the Church Fathers, especially from Augustine of Hippo, rather than from the Schoolmen.
[4] While Chancellor Ruard Tapper and Josse Ravesteyn, Professor of Theology were at the Council of Trent, Baius and Hessels took the occasion to introduce new methods and new doctrines.
Not content, however, with a mere change of method they began to show their contempt for traditional opinions, and in a short time alarming rumours were in circulation both inside and outside the university that their teaching on Original Sin, Grace, and Free-will, was not in harmony with the doctrine of the Church.
[5] As the dispute grew more heated and threatened to have serious consequences for the university and the country, in 1563, the Archbishop of Mechlin, Cardinal Granvelle, believing that the absence of the two professors might lead to peace, induced both to accompany theology professor the elder Cornelius Jansenius (later Bishop of Ghent) to the Council of Trent as the theologians of the King of Spain (1563).
Even at Trent the Scholastic party found fault with his departure from the beaten tracks of learning; after his return the attacks continued.