The rules for common priests were more strict than for the high priest, who represented all of Israel, including other priests (Leviticus 21:1–4).
The priest must always keep his hair neat and not tear his clothing in mourning. This ensured he was always ready to serve. While a common priest could marry a widow, the high priest could only marry a virgin. This ensured that future high priests and common priests from that union would have a clear lineage (Leviticus 21:15).