We are accustomed to seeing the order of these words reversed (doctrine and practice), and rightly so. In his epistles, the Apostle Paul generally begins with teaching doctrine and then applying the doctrine to daily life. Accordingly, Question 2 of the Westminster Shorter Catechism asks, “What do the scriptures principally teach?” The answer puts doctrine first, and practice second: “The Scriptures principally teach what man is to believe concerning God, and what duty God requires of man.” The order is important. No one can perform a good work to the glory of God until he first knows the living and true God and receives the Mediator whom He has provided.
However, Scripture gives examples of errors in practice leading to errors in doctrine. For example, when the Apostle Peter was in Antioch, he regularly ate with Gentile believers. But when certain Jewish believers came from Jerusalem, he withdrew and separated himself from the Gentile believers, fearing those who were of the circumcision (Gal. 2:12). The apostle Paul immediately saw the danger: “But when I saw that they walked not uprightly according to the gospel, I said unto Peter before them all, If thou being a Jew, livest after the manner of Gentiles and not as do the Jews, why compellest thou the Gentiles to live as do the Jews?” In other words, Peter had been correctly living as if the ceremonial laws were not necessary for salvation, but now that he was among Jewish believers from Jerusalem, he was living as if they were necessary. Peter believed in justification by faith alone without the works of the law, but his practice was contradicting this doctrine. Paul saw that his practice would lead to serious errors about justification and therefore did not hesitate to correct it publicly.
In Numbers chapters 22 through 25, we have another example of how practice affects doctrine. The king of Moab, Balak, felt threatened by the children of Israel and tried to hire Balaam to curse the children of Israel. But Balaam found he could not: “Behold, I have received a commandment to bless: and He hath blessed, and I cannot reverse it” (Num. 23:20). Much to the frustration of Balak, Balaam proceeded to bless Israel again and again.
But Balaam loved the wages of unrighteousness and was determined to find a way to weaken Israel and obtain Balak’s promised reward. He saw that there was no way to defeat this “Church in the wilderness” (Acts 7:38) except by getting them to provoke their Almighty God. In Numbers 31:16 we discover that it was Balaam’s idea to send the Moabitish women to Israel to entice the men to sin, bring them to worship the gods of the Moabites, and thereby bring divine displeasure upon the Church. The displeasure of God, more than anything else, would make her an easy prey for her enemies. But notice the sequence: first the Moabitish women draw the men into immorality (an error in practice) and then they get them to worship their false gods (an error in doctrine).
Some might say that this is an extreme example. But it reveals a principle of vital importance: any sin that is tolerated in our hearts and lives will bring darkness into our minds. “A little leaven leaveneth the whole lump” (Gal. 5:9). In his poem The Progress of Error, William Cowper observed,
“Faults in the life breed errors in the brain,
And these reciprocally those again.
The mind and conduct mutually imprint
And stamp their image in each other’s mint.”
No student of church history will deny that Protestant churches have departed from doctrines that were widely accepted during the Reformation. Lovers of the truth will ask, How did this happen? One of the answers will be that worldliness entered the Church and made many of her members indifferent to the vigorous defense of sound doctrine.
For this reason, you will find many articles on this website and in Free Presbyterian magazines about various practical matters. Sound doctrine and holy living go together; what God has joined together, let no man put asunder. Let this be a warning to all modern Reformed writers who ably defend sound doctrine, but feel no shame in relating their favourite movies, professional sports teams, and worldly songs – all promoted by enemies of truth and godliness.