The clause “that which was the most sad and lamentable” is build upon the idea of the chapter title “The Starving Time” because one of the reasons why half the population died was because they were starving for not just food but basic comforts like shelter and warmth.
Bradford is referring to the death of half of the pilgrims due to winter, starvation, and diseases.
The mood of the chapter is somber and tragic which is in direct contrast to the energetic mood at the start of Chapter 9. Chapter 9 starts with “In sundry of these storms, the winds were so fierce...but were forced to hull for divers days together”. Although in both the instances they are struggling and refuse to give up, the mood in the latter is less hopeful.