Numbers 19.14 had said that if an Israelite touched a dead body in a tent, then that living person was unclean for seven days, and had to go through a ceremony to become clean again.
Two verses later, the Lord let Israel know that this applied to touching dead bodies in the open field also,
“Whoever in the open field touches one who is slain by a sword or who has died, or a bone of a man, or a grave, shall be unclean seven days” (Numbers 19.16).
If the person had been killed, or simply died, or even if the person had been dead long enough that only the bones remained, or if the Israelite touched a grave, then he or she was unclean for seven days.
Why was such a person unclean for seven days? The Bible does not specify the reason, unless I have missed it, but it was simply what the Lord had determined and the Israelites had to follow His instructions to be clean again.
- Numbers 19.14, 15 – Everything unclean for seven days after contact with a dead body (sevensinthebible.com)
- Numbers 19.11, 12 – Seven days for purification after touching a dead body (sevensinthebible.com)
- Numbers 6.9 – Nazirite re-consecrated with a seventh-day shaving (sevensinthebible.com)
- Numbers 16.49 – Incidental reference 14,700 dead (sevensinthebible.com)