Scripture and Tradition are necessary for the fullness of Truth. If we place our faith in Scripture alone, we are missing the living Tradition and are not entirely living in the light.
"Sacred Scripture is the speech of God as it is put down in writing under the breath of the Holy Spirit. And [Holy] Tradition transmits in its entirety the Word of God which has been entrusted to the apostles by Christ the Lord and the Holy Spirit." (CCC 81)
The Apostles handed down the teachings and examples they received from Jesus and the Holy Spirit to the Church. The Catholic faith does not rely solely on the Holy Scriptures but accepts with equal value and devotion Scripture and Tradition to interpret Divine Revelation. Want to know why the first generation of Christians didn't rely on Scripture alone? They didn't have a written New Testament. The New Testament comes from the living Tradition.
Not all tradition is Sacred Tradition. Tradition, with a capital T, refers to Sacred Tradition. Catholic Tradition is different from small t traditions that are merely customs of local churches, and are not part of Divine Revelation.
The successors of the Apostles are servants to the Scriptures and Tradition. They have been entrusted with preserving, teaching, and practicing the faith that has been passed on to them. Priests preach homilies based on the Divine Revelation of the Scriptures, not their feelings or personal revelation about a scripture passage. When you attend a Mass, the prayers and the breaking of the bread are the same in every Catholic Church. The Scriptures, along with Tradition, complement one another to reveal who God is, allowing us to know Him and love Him. The Holy Spirit is active in the Tradition of the Church; that is why it is the living Tradition. It is not something that remains in the past but is actively working in the lives of the faithful today. #livinglent2