Q. Have you any other way of proving that the (Catholic) Church has power to institute festivals of precept?
A. Had she not such power, she could not have done that in which all modern religionists agree with her;—she could not have substituted the observance of Sunday the first day of the week, for the observance of Saturday the seventh day, a change
for which there is no Scriptural authority. Rome claims to have made the change. Look up A Doctrinal catechism by Rev. Stephen Keenan Pg. 174
The scriptural authority is n the Gospels and Book of Acts. The Messiah gave the power to bind and loose to the Apostle Peter, and by extension the other Apostles (and by implication their successors). The one holy catholic and apostolic Church has enjoyed the Holy Spirit in this world (for the Messiah sent the Comforter to His church).
The Apostle to the Gentiles wrote about the Gentiles who desire to come under the Law of Moses independent of the one holy catholic and apostolic Church. It is fairly straight forward for Gentiles.