To make atonement ( Exodus 32:30) means to obtain a covering for sin. [source][source][source]
We see Moses" great love for the Israelites as their mediator in his willingness to die for them (cf. Romans 9:3). Being blotted out of God"s book may refer to physical death. Alternatively the book could refer to the register of those loyal to Yahweh and thereby deserving His special blessing (cf. Psalm 69:28; Isaiah 4:3; Ezekiel 13:9; Daniel 12:1; Malachi 3:16). [1] God explained a principle of His dealings with people here. Individual sin brings individual responsibility that leads finally to individual judgment (cf. Ezekiel 18:4). God was not saying that everyone will bear the punishment for his own sins precluding substitution, but everyone is responsible for his own sins. He chose not to take Moses" life as a substitute for the guilty in Israel since this would not have been just. Moses being a sinner himself could not have served as a final acceptable substitute for other sinners in any case. [source][source][source]
God promised Moses that He would not abandon His people for their sin ( Exodus 32:34), but when their rebellion was full (at Kadesh Barnea, Numbers 14:27-35) He smote those of them who remained ( Exodus 32:35). [2][source]