The phrase "a trustworthy saying" appears in the New Testament, primarily in the pastoral epistles attributed to the Apostle Paul. These sayings are concise, doctrinally significant statements that were likely used in the early Christian communities for teaching and affirmation of faith. The Greek term used is "πιστὸς ὁ λόγος" (pistos ho logos), which can be translated as "faithful is the word" or "this is a trustworthy saying."

Occurrences in the New Testament:

1. 1 Timothy 1:15 · "This is a trustworthy saying, worthy of full acceptance: Christ Jesus came into the world to save sinners, of whom I am the worst."
This saying emphasizes the core Christian belief in the redemptive mission of Jesus Christ. Paul uses it to highlight the grace and mercy of God, acknowledging his own past as a persecutor of Christians and underscoring the transformative power of Christ's salvation.

2. 1 Timothy 3:1 · "This is a trustworthy saying: If anyone aspires to be an overseer, he desires a noble task."
Here, the saying pertains to church leadership, specifically the role of an overseer or bishop. It underscores the importance and honor of church leadership, setting a standard for those who seek such positions.

3. 1 Timothy 4:8-9 · "For physical exercise is of limited value, but godliness is valuable in every way, holding promise for the present life and for the one to come. This is a trustworthy saying, worthy of full acceptance."
This passage contrasts the temporary benefits of physical exercise with the eternal value of godliness. The trustworthy saying affirms the comprehensive benefits of living a godly life, both in the present and in eternity.

4. 2 Timothy 2:11-13 · "This is a trustworthy saying: If we died with Him, we will also live with Him; if we endure, we will also reign with Him; if we deny Him, He will also deny us; if we are faithless, He remains faithful, for He cannot deny Himself."
This saying is a poetic and doctrinal affirmation of the believer's union with Christ. It speaks to the hope of resurrection, the call to perseverance, the consequences of denial, and the unwavering faithfulness of Christ.

5. Titus 3:4-8 · "But when the kindness of God our Savior and His love for mankind appeared, He saved us, not by the righteous deeds we had done, but according to His mercy, through the washing of new birth and renewal by the Holy Spirit. This is a trustworthy saying."
This passage highlights the doctrine of salvation by grace, emphasizing God's mercy and the transformative work of the Holy Spirit. The trustworthy saying serves as a reminder of the foundational Christian belief in salvation not by works, but by divine grace.

Theological Significance:

The "trustworthy sayings" serve as doctrinal anchors within the pastoral epistles, providing concise summaries of key Christian beliefs. They reflect the early church's emphasis on sound teaching and the transmission of apostolic doctrine. These sayings were likely used in catechesis and liturgy, helping to shape the faith and practice of early Christian communities. Each saying encapsulates a significant aspect of Christian theology, from Christ's redemptive work to the call for godly living and the hope of eternal life.