"...Faith and grace, however, do not supress our conditioning. Consequently, grace does not eliminate our heredity, our instincts, or our psychological make-up. Normally grace should transform our conditioning, but this takes time. This can be seen in converts. There is a grace of conversion, and at that moment everything seems easy. They are "struck by lightning" - as when one falls in love. A few years later, however, things become difficult. This does not mean that there is regression. It simply means that the psyche has not changed, that instincts have not changed, that it takes time for God's grace to transform what one is. Grace is the yeast that must make the dough rise, but this does not happen overnight."
Extract from Wherever He Goes, Fr. Marie-Dominique Philippe, o.p., p.168.