Exodus 19:8

And all the people answered together
By their heads and representatives, the elders, summoned before Moses, to whom he declared the whole will of God; or this being communicated by them to their respective tribes and families, they were all of one mind; there was not a contradicting voice among them, they all gave the same answer, or all united in returning for answer what follows:

all that the Lord hath spoken we will do;
obey his voice in all things he directs unto, or commands to be done, and keep the covenant he should make with them, and observe whatever was required on their parts; which was well spoken, if with the heart, and if, under a consciousness of their own weakness, they had expressed their desire of dependence upon the grace of God to enable them to perform, see ( Deuteronomy 5:28 Deuteronomy 5:29 ) . The Septuagint version adds, "and we will hear", or be obedient, as in ( Exodus 24:7 ) :

and Moses returned the words of the people unto the Lord;
not for his information, who knew very well what they had said, but for the discharge of his office as a mediator and messenger between God and them: this, according to Jarchi, was on the third day of the month.