לְמַ֛עַן נַסּ֥וֹת בָּ֖ם אֶת־יִשְׂרָאֵ֑ל הֲשֹׁמְרִ֣ים הֵם֩ אֶת־דֶּ֨רֶךְ יְהוָ֜ה לָלֶ֣כֶת בָּ֗ם כַּאֲשֶׁ֛ר שָׁמְר֥וּ אֲבוֹתָ֖ם אִם־לֹֽא׃
為要藉著他們試驗以色列，看以色列人是否會像他們列祖那樣，謹守永恆者的道，行在其中。»
Rashi
Whether they observe. The letter ה is vocalized with the abridged pasach,15This vocalization is used to express inquiry. as it expresses the inquiry involved in testing.
Metzudat David
IN ORDER TO TEST: It wants to teach that because of this, Hashem chose this punishment, and not others in order to test Israel if they will serve their GD or if not. And this is why its written "if they will guard."