Let us look at the way holiness was to be attained under the old covenant. God said, “You shall be holy; for I am holy” (Leviticus 11:44). All of Leviticus 11 enumerates complicated regulations regarding what to eat, what to wear, and what makes one clean or unclean.
God’s requirement was to “consecrate yourselves” (Leviticus 11:44). But you find out from this chapter that maintaining holiness was very complicated. There was a series of the most involved regulations.
These also shall be unclean to you among the creeping things that creep on the earth: the mole, the mouse, and the large lizard…; the gecko, the monitor lizard, the sand reptile, the sand lizard, and the chameleon….Whoever touches them when they are dead shall be unclean until evening. (Leviticus 11:29–31)
According to this regulation, for instance, if a mouse died and someone picked it up by the tail, he would be unclean until that evening. But Scripture goes on to give further regulations about the container the mouse might fall in and the article of clothing it might touch, then gives instructions on how to deal with the uncleanness. Observing all of these regulations would be a full-time job.
God said that if you succeeded in following these rules, you would be holy. But if you were going to attain holiness by keeping a set of rules, you would have to keep all the rules all the time. You could not omit one at any time. But thank God that He provided a better way—because keeping all these rules is impossible for sinful humans.