Musar sobre Deuteronómio 5:19

I have found the following comment by Nachmanides on the commandment לא תשא את שם ה' אלוקיך לשוא: "They heard the first two commandments from G–d directly. This is why the sages said that these two commandments are the essence of all the Commandments. How do we reconcile this with the view of Rabbi Eliezer who points out that the Torah says in Exodus 20,1: 'G–d spoke all these words?' Moses said to the people in Deut. 5,19: את הדברים האלה דבר ה' אל כל קהלכם בהר מתוך האש. 'G–d spoke these words to your entire congregation at the Mountain out of the fire.' The Torah (Moses) continues there: 'He inscribed them on two stone tablets and gave them to me' (Moses). This clearly implies that what G–d inscribed on the tablets was exactly what He had said to the people!