In Protestantism, the continental reformers criticized fasting as a purely external observance that can never gain a person salvation. Martin Luther believed that a Christian may choose to fast individually as a spiritual exercise to discipline his own flesh, but that the time and manner of fasting should be left to the individual's discretion, thus he rejected the collective diet rules and prohibitions imposed by the canon law of the Catholic Church.[41] This position was upheld by Lutheran churches, in that collective fasting was not officially enforced, whereas individual voluntary fasting was encouraged.