Here is a quick word study through the NT on how positively or negatively practical doctrine is. Doctrine influences your behavior.
“Now we know that the law is good, if one uses it lawfully, understanding this, that the law is not laid down for the just but for the lawless and disobedient, for the ungodly and sinners, for the unholy and profane, for those who strike their fathers and mothers, for murderers, the sexually immoral, men who practice homosexuality, enslavers, liars, perjurers, and whatever else is contrary to sound doctrine, in accordance with the gospel of the glory of the blessed God with which I have been entrusted.” (1 Timothy 1:8-11 ESV)
Lawless deeds are contrary to sound doctrine.
“And he gave the apostles, the prophets, the evangelists, the shepherds and teachers, to equip the saints for the work of ministry, for building up the body of Christ, until we all attain to the unity of the faith and of the knowledge of the Son of God, to mature manhood, to the measure of the stature of the fullness of Christ, so that we may no longer be children, tossed to and fro by the waves and carried about by every wind of doctrine, by human cunning, by craftiness in deceitful schemes.”
(Ephesians 4:11-14 ESV)
God gave the church gifted persons to teach them sound doctrine so that they are not carried about by every wind of doctrine. There is a lot of bad doctrine we need to hold fast to good doctrine.
For more check this out Doctrine.