Final answer:
The key division in the Politburo was over industrialization policies. Sergei Kirov's opposition to Stalin posed a significant threat due to his power base in Leningrad. Stalin's role was theoretically equalized with other secretaries, affecting his autocratic authority.
Step-by-step explanation:
The key point of division within the Politburo was the pace of industrialization and the policy of forcible grain seizures. Stalin wanted to maintain rapid industrial growth, whereas others pushed for more moderate policies.
The threat posed by Sergei Kirov's alignment with the opposition to Stalin was significant because Kirov had strong support within the Leningrad party and his rising popularity could rival Stalin’s authority.
Kirov played a significant role within the Soviet Communist Party as a leader of the Leningrad party and had been one of Stalin's closest allies before siding with the opposition.
A change occurred in Stalin's position as General Secretary when he and other secretaries were made of equal rank, which, in theory, meant his leadership role was diminished.
The redistribution of power affected Stalin’s authority theoretically by placing him on equal footing with other secretaries but may have also been a strategic move by Stalin to diffuse blame for the USSR’s problems.