What happened to Israel and the twelve because of Israel's unbelief?
Because of Israel's unbelief, the Twelve's authority slipped away, and Israel lost what it had. A few years after this was written, the Temple and Jerusalem were destroyed, and Israel went into dispersion among the nations. The Twelve had been Jesus' chosen vessels, but Israel's rejection meant they lost that position.
Les teaches that the men in Jerusalem were Peter, James, John, and the rest, the Twelve. The writer says he did not give place by subjection to them, no, not for an hour, so the truth of the gospel might continue with the Gentiles. Those who seemed to be somewhat were the Twelve, Jesus' chosen vessels, but Israel had rejected it all and was slipping away. Their authority had slipped through the cracks, and his had ascended. Les points out that just a few years after this was written, the Temple and Jerusalem would be destroyed, and Israel would go into dispersion among the nations. They had their time, but because of Israel's unbelief they lost it.
But of these who seemed to be somewhat, (whatsoever they were, it maketh no matter to me: God accepteth no man’s person:) for they who seemed to be somewhat in conference added nothing to me: