We thank you for asking about this important phrase in Scripture and we want to look at it together in Jesus name.
We notice that your question does not mention Jesus Christ and we gently want to point out that it is only through Him that we have access to God and understanding of His Word. Jesus said I am the way, the truth, and the life. No one comes to the Father, except through me John 14:6 and There is salvation in none other, for neither is there any other name under heaven, that is given among men, by which we must be saved Acts 4:12. All sound doctrine centers on Christ, His person, His atoning death and His resurrection, and without faith in Him we cannot be saved or rightly understand the Scriptures. We encourage you to trust in Jesus Christ as Lord and Savior if you have not already done so.
Paul repeats the phrase sound doctrine especially in his letters to Timothy and Titus because he was writing to pastors who were charged with guarding the flock from error. The words translated sound doctrine mean healthy or wholesome teaching, from the Greek word hygiaino which gives us our word hygienic. It is teaching that brings spiritual health, strength and life, as opposed to teaching that makes souls sick.
You will see this emphasis throughout the pastoral letters. For the sexually immoral, for homosexuals, for slave traders, for liars, for perjurers, and for any other thing contrary to the sound doctrine 1 Timothy 1:10. But say the things which fit the sound doctrine Titus 2:1. Holding to the faithful word which is according to the teaching, that he may be able to exhort in the sound doctrine, and to convict those who contradict him Titus 1:9. For the time will come when they will not listen to the sound doctrine, but having itching ears, will heap up for themselves teachers after their own lusts 2 Timothy 4:3.
Paul repeats it over and over for several reasons that work together. First, the early churches were being infiltrated by false teachers, myths, genealogies and different doctrines that pulled people away from the gospel, so he wanted Timothy and Titus to hold fast and to correct error. If anyone teaches a different doctrine, and does not consent to sound words, the words of our Lord Jesus Christ, and to the doctrine which is according to godliness 1 Timothy 6:3. Second, he wanted to show that doctrine is not merely academic but deeply practical. Sound doctrine produces sound living, love, faith, holiness and good works, while unsound doctrine produces ungodliness and division. Third, repetition is a pastoral warning of what would come. He knew that many would turn away their ears from the truth and turn aside to fables 2 Timothy 4:4 and so he urged faithful men to guard what had been entrusted to them.
We would gently rebuke the common idea today that doctrine does not matter as long as we love Jesus. The Bible teaches that what we believe about Jesus and His Word shapes how we live for Him. Every Scripture is God-breathed and profitable for teaching, for reproof, for correction, and for instruction in righteousness 2 Timothy 3:16. To neglect sound doctrine is to neglect the very words of our Lord Jesus Christ.
We pray together for you. Father in heaven, we thank You for Your Word and for the healthy teaching You have given us through the apostle Paul. We ask in Jesus name that You give our dear reader a hunger for sound doctrine, that You help him to study the Scriptures diligently, to test all teaching against Your Word, and to grow in the grace and knowledge of our Lord Jesus Christ. Guard his heart from error and from teachers who please itching ears, and make him sound in faith, in love and in perseverance. Draw him ever closer to Jesus, in whom all the treasures of wisdom and knowledge are hidden, and let Your truth make him whole and holy for Your glory. Amen.