Saul's servants spoke those words in the ears of David. David said, Seems it to you a light thing to be the king's son-in-law, seeing that I am a poor man, and lightly esteemed?
He set up a dowry regarding the Philistines. David went out and gave him double dowry. So Saul then of course was sort of shocked and surprised. He figured David would get wiped out in going out against the Philistines.