Luke 4:32 (NIV)
Because His message had authority.
A saint's authority comes from God. As much as saints are commanded to respect local and Church leaders, they aren't the ones who certify the saint. The power to teach, preach, and rebuke with all authority (Titus 2:15) comes from God (John 21:15- 17) and doesn't require the Church's approval.
The present Church system of formally educating and ordaining ministers, although well-intentioned, is not scriptural. The Apostle Paul lays down some guidelines for appointing pastors, deacons, and elders (1 Timothy 3). However, no formal training was mandated. Paul himself was not taught by man but by the Holy Spirit for three years in the deserts of Arabia (Galatians 1:17). A formal ordination process by the Church to appoint clergy began in the 2nd century and became controversial.
The power to preach the gospel was invested in the clergy, and the rest were considered laity. Although some of us are called explicitly into the ministry (1 Cor 12:28), every saint is a minister of the gospel (1 Peter 2:9) and has the divine authority to spread the good news where they are. That authority does not come from any pastor or Pope but from the Lord Jesus Christ.