The words of God are clear and distinct, “Obedience is better than sacrifice.” “In vain do they worship me, teaching for doctrines the commandments of men,” (1 Sam. 15:22; Matt. 15:9). Every addition to his word, especially in this matter, is a lie. Mere “will worship” (ethelothreeskeia) is vanity. This is the decision, and when once the judge has decided, it is no longer time to debate.
John Calvin (2010-03-25). The Necessity of Reforming the Church (Kindle Locations 84-87).
It is a difficult thing as Calvin notes to pursuade the world that God has determined how he is to be worshipped. The problem is not our zeal but rather our obedience to God’s revealed will. Therein lies a problem when we take the opinion that we can approach God how we will rather than how he has already “willed”. Thank God for the mercy we have in Jesus. Therefore we are represented by the faithfulness of our federal head Jesus and spared the fate of Nadab and Abihu.