I will start the sharing with this one (spoilers ahead):
'To live in the present as best as we can and move on from the past.'
This applies to both the case when Tofu helped both Na and Nut to move away from their painful past, and be reconciled to each other, and making use of whatever time they have in the present (as Na's Alzheimer's meant that they won't have much time together), and also when Tofu passed away, and Nut having to move on in the present (while at the same time still keeping his love for Tofu - love is timeless).
In a way, Saen and Jan were also trapped in their past, because the former kept on regretting that Na wasn't the one he married, while Jan kept on hoping and pining that her husband would finally love her instead of Na. Their inability to move on was what caused (directly or indirectly) some of the most important tragedies in the entire story of the series, namely Saen killing Sib, Na's husband and his own brother, and Jan killing Tofu with the poisoned drink.
