How do we know the authority of the decrees in Acts 15?

The decrees in Acts 15 are presented as authoritative because they are believed to be inspired by the Holy Spirit. Acts 15:28 states that it seemed good to the Holy Spirit and to the apostles to lay upon the Gentile believers no greater burden than these necessary things. This highlights the divine origin of the instructions, as the early church recognized the guidance of the Holy Spirit in determining what was essential for the faith and conduct of believers. Adhering to these decrees fosters unity among believers and ensures they remain grounded in truth, reflecting the sovereignty of God in guiding His church.