Matthew Poole and continuators on Joshua 2:17

17 And the mensaid unto her, We will be blameless of this thine oath, which thou hast made us swear:

Or, had said; namely, before she let them down; it being very improbable, either that she would dismiss them before the Condition was expressed and agreed; or that she would discourse with them, or they with her, about such secret and weighty things after they were let down, when others might over-hear them; or that she should begin her discourse in her Chamber, and not finish it till they were gone out of her House. Obj. They spoke this after they were let down; for it follows, v. 18. this—thread—which thou didst let us down by. Ans. Those words may be thus rendred, which thou dost let us down by; i. e. art about to do it: it being frequent for the Preter Tense to be used of a thing about to be done, by an Enallage of Tenses, as Iosh. 10. 15.

i. e. Free from guilt or reproach if it be violated, namely, if the following Condition be not observed.