Rashi on Deuteronomy 32:20/רש"י על דברים ל״ב:כ׳

1מה אחריתם [I WILL SEE] WHAT THEIR END SHALL BE — i.e. what will come upon them in the end.

2כי דור תהפכת המה FOR THEY ARE A GENERATION OF PERVERSITY - i.e. they change (הפך) My goodwill into anger.

3לא אמן בם means, My training is not evident in them, for I showed them the good way and they have deviated from it.

4אמן is of the same meaning as in (Esther 2:7) “And he brought up (אמן) Hadassah”. Nouriture in old French — Another explanation of אמן: it has the same meaning as אמונה, faithfulness, as the Targum takes it (“in whom there is no faithfulness”). At Sinai they said, “We will do and we will hearken” and after a very short time they broke their promise and made the golden calf (Sifrei Devarim 320:6).