Sforno on Exodus 23:21/ספורנו על שמות כ״ג:כ״א

1השמר מפניו, not to offend his dignity. The word is used in a sense similar to Joshua 5,9 (the angel speaking) “remove your shoe from your foot!”

2ושמע בקולו, to follow in his footsteps, the reverse of what the Israelites had done (as reported) in Deuteronomy 1,28 when they were willing to listen and to follow the 10 spies who had declared that it was impossible to attain their objective, i.e. the conquest of the land of Canaan.

3אל תמר בו כי לא ישא לפשעכם, if even a single individual will sin, the punishment will include his fellow Jews. This is precisely what happened when Achan had stolen from the loot of Jericho and, because his sin had been covered up, Israel lost the first battle of Ai. (Joshua refers to this as a warning in Joshua 22,20. He reminds the people that Achan was not the only one punished for this sin but that G’d [presumably because He had invested His angel with such authority. Ed.] vented His anger at the entire nation.)

4כי שמי בקרבו, and it is not in his power to forgive offenses against My honor.