Matthew 23:4-7 “For they bind heavy burdens and grievous to be borne, and lay them on men’s shoulders; but they themselves will not move them with one of their fingers. But all their works they do for to be seen of men: they make broad their phylacteries, and enlarge the borders of their garments, And love the uppermost rooms at feasts, and the chief seats in the synagogues, And greetings in the markets, and to be called of men, Rabbi, Rabbi.”
Those who like to make up extra-biblical rules always have two characteristics: (1) After putting these great burdens on people, they do not have any sympathy, nor do they give those people any help. (2) These legalists always want the attention of men, the applause of men, and want others to think of them as “strict.”
It is wrong to add to the Bible for any reason. It is just as wrong of fundamentalists to add to the Bible as it is for a cult to do so. It is fine for a Christian to have rules for himself. We should all have standards for ourselves consistent with our personal convictions. However, Jesus condemned legalists who try to force their personal convictions on others when there is no clear statement of Scripture to support the rules.