**Catholic tradition (the priesthood)**
The priesthood is not the definition of Holy Tradition.
From the article for the second time:
What is Tradition?
In this discussion it is important to keep in mind what the Catholic Church means by tradition. The term does not refer to legends or mythological accounts, nor does it encompass transitory customs or practices which may change, as circumstances warrant, such as styles of priestly dress, particular forms of devotion to saints, or even liturgical rubrics. Sacred or apostolic tradition consists of the teachings that the apostles passed on orally through their preaching. These teachings largely (perhaps entirely) overlap with those contained in Scripture, but the mode of their transmission is different.
They have been handed down and entrusted to the Churchs. It is necessary that Christians believe in and follow this tradition as well as the Bible (Luke 10:16). The truth of the faith has been given primarily to the leaders of the Church (Eph. 3:5), who, with Christ, form the foundation of the Church (Eph. 2:20). The Church has been guided by the Holy Spirit, who protects this teaching from corruption (John 14:25-26, 16:13).
I’m already familiar with that. Just read from “the truth of the faith has been primarily given...” That’s the point. The Bible says Jesus is the foundation of faith, but the Catholic Church (priesthood) says Christ AND the Catholic Church leaders are the foundation.
If this be the case, then why isn't the Bible sufficient? They wrote these teachings down so we would have them for later. It's still about Christ today as it was then. The story of the NT hasn't changed.
While I agree the initial message was given to the apostles, you have to start somewhere, there is nothing to suggest that only the apostles are the ones who can continue to share/teach the Gospel. This would contradict the teachings regarding spiritual gifts which are given to all followers of Christ in one form or another according to 1 Corinthians. Some apostles, teachers, some prophets, and so on.
Do we really think the initial apostles were the only ones able to share the Gospel? Acts 8:4 records that those who had been scattered went about preaching the word. Later in Acts 11:19-20 we learn they where in Phoenicia, Cyprus and Antioch. They spoke to the Jews first and then men from Cyprus and Cyrene who went to Antioch and began speaking to the Greeks preaching the Lord Jesus Christ.
So here we have evidence that non-apostles can preach and teach just as the apostles did. Why? They're preaching and teaching the same message.
The church grows by people like you and me sharing the Gospel with people we encounter. It happens everyday all around the world.
Praise God that He allows us to share in His Kingdom and to share His glorious offering of forgiveness through His Son Jesus Christ!