Sforno on Numbers 14:34/ספורנו על במדבר י״ד:ל״ד

1במספר הימים, we have a rule in halachah that שלוחו של אדם כמותו that when one appoints someone to act on one’s behalf the appointee is regarded as an extension of the one who appointed him. The spies had therefore not acted on their own, but as the people’s agents. Hence Moses, i.e. G’d, addresses the people as the instigators of this disaster. Their initial sin had consisted in wanting to find out if the land could be conquered.

2יום לשנה, on a specific day each year, i.e. the ninth of Av, according to the sages in Taanit 30.

3תנואתי; you will find out what it means to try and thwart My plans. (a reference to verse 43 when this “self-fulfilling “ prediction came true.).