Charles Ellicott Commentary 1 Samuel 17:28

"And Eliab his eldest brother heard when he spake unto the men; and Eliab`s anger was kindled against David, and he said, Why art thou come down? and with whom hast thou left those few sheep in the wilderness? I know thy pride, and the naughtiness of thy heart; for thou art come down that thou mightest see the battle." — 1 Samuel 17:28 (ASV)

And Eliab’s anger was kindled against David. There were probably many years between the ages of the eldest and youngest of these eight brothers, and this jealous anger was, undoubtedly, nothing new for Eliab. The casual mention (1 Samuel 17:34) of the boy’s prowess when the lion and the bear attacked his father’s flock tells us that David’s boyhood and youth had been no ordinary one, and Eliab’s jealous disposition had undoubtedly often been aroused.

Probably, too, the envious elder brother well remembered the visit of the great seer to Bethlehem. He recalled how Samuel, for some mysterious and still unknown reason, had anointed this younger brother of his and chosen him to be his pupil and companion. Had David now come with power unknown to Eliab to perform some startling, daring deed?