Here Paul is refuting the false worship which men may impose on others. Will-worship is when the human factor is the agent by which worship is dictated. Often, this is when the pew dictates to the pulpit what is preached, and how the worship is structured. Unfortunately, the church then becomes like the world, instead of the conversion of souls to make the world the church. Worship then becomes a matter of taste, and convenience.
Human desire becomes the deciding factor.
Imagine if Nadab and Abihu were allowed to come and visit the contemporary church they would fall to the ground and weep bitterly knowing that their sin is still carried on today with acceptance. The Puritans desired simple, biblical worship. They were not interested in putting on a show. When Elijah was on Mt. Carmel in 1 Kings 18, he asked the people if they were ready to follow God or Baal. When posed with the question, the people were silent.