The last six games look like this:
The Seahawks will only be favored to win in two of those six games (CAR, STL), and one of those teams has already beat Seattle rather easily. The Carolina game is the best bet of the bunch, so let's call that one win. The STL game should be a win, so let's call that two. That would be seven wins, and the tie-breaker over STL. That is probably enough to win the division. Games @SF and home against KC are about equal in difficulty. Dismiss SF at your own risk, and road games are always tough. Splitting those two gets the Seahawks to eight wins. Hosting ATL and traveling to TB will be major tests, but not any harder than facing the Saints last week. Losses in both games are expected, but projecting too far ahead is tough given the injury situation with Seattle. Colin Cole, Mike Williams, and Left Guard'O'The'Day, could be having everyone feeling rosy or red-faced.
If things go largely as expected, there will be wins against CAR and STL, and losses to TB and ATL. Losing to KC would mean a win in SF would be required to get to 8 wins, and clinch the division. Nobody wants to bet the season on a road game. Winning against the Chiefs makes the 49ers game a bonus match that could be part of a 3-game win streak, lifting the team to 8-5 with three games to go, and probably clinching the division early. Going that route means choices can be made about resting players, installing new schemes, or possibly even going for a first round bye (unlikely) or drawing the lower-seeded wildcard team.
The Seahawks do not need to win on Sunday, but doing so raises the ceiling on a season has seen a dizzying collection of ups and downs.