Good point, JessicaDellEra. BTW: this construction (with the preposition expressing obligation) goes back to Mishnaic Hebrew, e.g., Yad 4.3 עליך ראיה ללמוד, "you have to provide evidence," lit. "upon you is evidence to teach." The text concerns a tithe; Danby renders with "thou must bring forth proof." Cf. Ps 56:13 עלי נדריך, "your vows are upon me," i.e., I owe them.