“‘And they stood at the bottom of the mountain.’ Rabbi Abdimi Bar Hama Bar Hasa said, ‘This teaches that He forced the mountain on them like a cask and said to them, ‘If you accept the Torah, very well; and if not, there will it be your burial.’ Rabbi Aha Bar Yaakov said, ‘This presents a strong protest against the Torah.’ Raba said, ‘Nevertheless, the generation received it in the days of Ahasuerus, for it is written, ‘the Jews observed and accepted,’ they observed what they had already accepted’’” (Shabbat [Sabbath] 88a).
In the Tosfot, “He forced on them… although they already preceded ‘We will do’ to ‘We will hear,’ lest they would regret when they saw the great fire when their soul departed. This is as he said, ‘Did You not force on us the mountain like a cask?’” (Avoda Zarah, 2b), meaning that had He not forced them, they would have repentance. But here he says that they protested against the Torah, meaning for not receiving it, but in that they did not observe it there is repentance.
We should interpret the meaning of forcing on them the mountain like a cask. We should know that as there is coercion by suffering, there is coercion by pleasure. One who wants his friend to do what he wants, his friend must comply in two ways: either because of suffering, when he is afraid of him that if he does not do his will, he will afflict him, or because of a pleasure that entices him to do what he wants.