Sforno on Exodus 4:23/ספורנו על שמות ד׳:כ״ג

1הנה אנכי הורג את בנך בכורכך, even though when it comes to the period known as קץ הימים, the end of the days of this planet, G’d will cause the kind of upheaval which will result in all the nations calling G’d by His chosen name and they will all serve Him without reservations, (Tzefaniah 3,9) even then Israel will still be special inasmuch as it is “My son.” I relate to Israel as a father relates to his son, not as a master relates to his servant, even the most benign of masters. A servant’s loyalty or “love” for his master is based on his expectations of reward, or his fear of punishment, not so a son’s loyalty and love. An additional reason for My preference for Israel is the fact that it is My firstborn son, i.e. it is the first nation to accept My position as Creator, King, Master in this universe. At a time when all the other nations were still following their misguided theologies, only the Jewish people proclaimed Me exclusively as their G’d and lawgiver. (compare Micah 4,5).