John Gill Commentary 1 Samuel 17:27

"And the people answered him after this manner, saying, So shall it be done to the man that killeth him." — 1 Samuel 17:27 (ASV)

And the people answered him after this manner
Told him what was proposed to be done in honour to the man that should attempt to kill him, and succeed:

saying, so shall it be done to the man that killeth him ;
as before related, that he should be enriched, marry the king's daughter, and his family be ennobled, (1 Samuel 17:25) .