15. On the seventh day. The says “on the fourth day.” This corresponds to the latter part of 14, which states that they tried to solve the riddle for three days.
Declare unto us. They meant that Samson would declare it through his wife, who was to secure the information and then tell them.
Lest we burn thee. The Philistines were brutal and treacherous even to their own people. Rather than lose a wager, they forced the woman with threats to aid them. It was no idle threat, for later they actually burned her and her father (see 15:6).