Under old covenant law, ritual uncleanness prevented a person from participating in fellowship offerings and feasts (see Leviticus 7:20–21). There were various things that could have caused such a state of uncleanness. They are specified in detail in Leviticus 11:1 – 17:16.
26 Yet Saul did not say anything that day, for he thought, “Something has happened to him. He is not clean; surely he is not clean.”