Albert Barnes Commentary Daniel 9:11

"Yea, all Israel have transgressed thy law, even turning aside, that they should not obey thy voice: therefore hath the curse been poured out upon us, and the oath that is written in the law of Moses the servant of God; for we have sinned against him." — Daniel 9:11 (ASV)

Indeed, all Israel has transgressed... - Embracing not only the tribe and the kingdom of Judah, but the whole nation. The calamity, therefore, had come upon them all.

Even by departing - By departing from your commandments; or by rebellion against you.

That they might not obey your voice - By refusing to obey your voice, or your commands.

Therefore the curse is poured upon us - As rain descends, or as water is poured out. The "curse" here refers to what was so solemnly threatened by Moses in case the nation did not obey God .

And the oath that is written in the law of Moses... - The word here rendered "oath" (שׁבועה shebû‛âh) means, properly, a "swearing," or "an oath;" and hence, it is either an oath of promise as in a covenant, or an oath of cursing or imprecation—that is, a curse. It is evidently used in the latter sense here (see Gesenius, "Lexicon").

Daniel saw clearly that the evils threatened by Moses (Deuteronomy 28:0) had actually come upon the nation. He also saw just as clearly that the cause of all these calamities was that which Moses had specified. Therefore, he frankly and penitently confessed these sins in the name of the whole people and earnestly pleaded for mercy.