Why did Jael give Sisera milk and not water as he requested?
"However, Sisera had fled away on foot to the tent of Jael, the wife of Heber the Kenite; for there was peace between Jabin king of Hazor and the house of Heber the Kenite. And Jael went out to meet Sisera, and said to him, "Turn aside, my lord, turn aside to me; do not fear." And when he had turned aside with her into the tent, she covered him with a blanket. Then he said to her, "Please give me a little water to drink, for I am thirsty." So she opened a jug of milk, gave him a drink, and covered him. And he said to her, "Stand at the door of the tent, and if any man comes and inquires of you, and says, 'Is there any man here?' you shall say, 'No.'" Then Jael, Heber's wife, took a tent peg and took a hammer in her hand, and went softly to him and drove the peg into his temple, and it went down into the ground; for he was fast asleep and weary. So he died. And then, as Barak pursued Sisera, Jael came out to meet him, and said to him, "Come, I will show you the man whom you seek." And when he went into her tent, there lay Sisera, dead with the peg in his temple. So on that day God subdued Jabin king of Canaan in the presence of the children of Israel" (Judges 4:17-23).
There can be several reasons. One, she gave him more than he requested. He asked only for a little water, but she gave him rich milk to drink. In recounting the events, Deborah said, "He asked for water, she gave milk; She brought out cream in a lordly bowl" (Judges 5:25). By treating him so well, he assumed that she was on his side and that he was safe. Having a full stomach also makes a person more tired, especially after a hard day. All this combined to cause Sisera to fall asleep without too much worry about being attacked. Little did he expect an attack from the woman who was treating him so kindly.