Rashi on Exodus 3:2/רש"י על שמות ג׳:ב׳

1בלבת אש means IN A FLAME OF FIRE, i. e. in the very heart of (לב) the fire. Similarly is לב used of inanimate objects in: (Deuteronomy 4:11) “in the heart of (לב) heaven”; (II Samuel 18:14) “in the midst of (לב) the terebinth”. Do not be puzzled by the ת, although the ordinary word for heart, לב. does not require the suffix ת in the construct form, because we have another example of this form, viz., (Ezekiel 16:30) “how weak is thy heart (לבתך)”.‎

2מתוך הסנה OUT OF THE MIDST OF A BUSH (a thornbush) — and not from any other tree, in accordance with the idea (Psalms 91:15) “I will be with him in trouble” (Midrash Tanchuma, Shemot 14).

3אֻכָּל means DEVOURED, eaten. It is of the same grammatical form as, (Deuteronomy 21:3) “which hath not been wrought with (עֻבַּד)”; (Genesis 3:23) “whence he was taken (לֻקַח):