The authority of the Apostles functions in much the same way as the authority Christ Himself had received from God the Father. It’s just like when a diplomat speaks for the chief executive of their country back home: the words of the diplomat function as the words of the executive, regardless of who literally says them. Christ spoke for God, and the Apostles spoke for Christ.

If you reject the teachings of the Apostles as somehow not having the same authority as those of Christ, you essentially reject Christ and God the Father.