Sforno on Exodus 3:4/ספורנו על שמות ג׳:ד׳

1וירא ה' כי סר לראות, When G’d saw that Moses took a deeper interest in the phenomenon,

2ויקרא אליו אלוקים, to explain the phenomenon to him, in accordance with the well known principle ofהבא לטהר מסיין אותו, “when someone wants to purify something impure one extends a helping hand to him “ A well known example of this is Exodus 19,3 where we find that as soon as Moses ascended the mountain G’d descended toward him.