The confrontation between Jael and the fleeing general Sisera was not a moment of simple hospitality, but a brilliant display of psychological and physical tactics. Every action taken by Jael was carefully calculated to disarm, exhaust, and ultimately defeat her enemy.
When Sisera asked for water, Jael instead provided milk. The primary approach among commentators is that the milk was intended to weigh him down, cloud his mind, and induce a deep sleep born of exhaustion, ensuring he would not wake when she struck. Others suggest the substitution was a test of his alertness, checking to see if he would even notice the difference in taste [רש״י]. Furthermore, offering milk served to quiet his suspicions. By avoiding cold water, which can be harmful to an exhausted person, she created the illusion that she was genuinely concerned for his health and well-being [אלשיך].
The drink was presented in a large basin or bowl [מצודת ציון]. Most commentators understand this to be an exceptionally grand vessel, one truly fit for kings, commanders, and heroes. Serving the drink in such a prestigious bowl was a deliberate act of flattery, designed to show Sisera great respect and instill in him a false sense of absolute security [מצודת דוד, אלשיך]. Alternatively, this type of bowl may have been one typically used by prominent shepherds [רד״ק]. Another view suggests it was simply a standard water vessel, as water itself is sometimes described as mighty [רש״י].
Finally, Jael offered him cream or butter, the rich fat of the milk [מצודת ציון]. Some explain that this was not a separate dish, but rather that the milk itself was exceptionally rich and unskimmed, making the drink even more intoxicating and sleep-inducing [רלב״ג, רד״ק]. Others believe that after the initial drink, she served him actual butter to eat, completing the illusion of a royal feast [רד״ק, אלשיך]. Taking a completely different approach, one commentator notes that while milk might warm the body, butter cools it. By serving this cooling food, Jael ensured there would be no misunderstanding that she was trying to arouse his desires, thereby protecting her reputation as a righteous woman [אהבת יהונתן].