When Sisra escaped and hid in Yael's tent, he ordered Yael, a'h, to bring him water, but instead she gave him milk - מַיִם שָׁאַל חָלָב נָתָנָה
Sisera knew he was going to get killed and he purposely asked for water because he wanted to know...
מַיִם - מתי יבוא משיח - When will Moshiach come?
Yael gave him milk instead of water, thereby answering him:
חָלָב - חייבים לחזור בתשובה - We must repent!