John was convinced that his call was meant to give Jesus to the world. For this he was to be another Christ. Thus he was to bring the sinners to reconciliation before God. John was convinced that his particular mission was to turn back the many sinners from the path of sin, through his words and deeds. He was also of the firm conviction that he had been called to proclaim Jesus and his kingdom to the multitudes around the world. With this intention, Fr. Ukken was forming himself in the Christian virtues, thereby developing a priestly personality worthy of his higher calling. He learnt to acquire a strong will, seraphic love, ardent zeal, profound humility. In his endeavour to become a priest, alter christus, he grew in special devotion to the Eucharist, Sacred Heart, Blessed Virgin Mary, St Joseph and the Guardian Angel.
He specially willed that the central event of each day would be the reception of the holy Eucharist. He spent long hours in silent meditation before the Eucharist, which was edifying to his fellow priests. He always asked his sisters not to grieve the Sacred Heart. His spiritual diaries also are a testimonial to the filial devotion of Fr. John towards the Holy Mother. He addressed her as my dear mamma. We can also see in Fr. John the loyal devotion to St Joseph