The correct answer to this open question is the following.
Bradford contrasted the Puritans' behavior with that of the sailors' when they are ill and dying in that the sailors had denied Beer for the Puritans, so after drinking beer, they started to die. Bradford said that they had committed sin, that is why they were getting sick and dying. So for Bradford, sailors had been punished by God for not sharing the beer with Puritans.
Bradford's purpose in showing this contrast was that the people that had survived were chosen by God to establish the colony in the North American territory and that they would always be supported by God. The Puritans traveled to the American in the Mayflower ship, where they encountered technical problems and bad weather conditions.