The firewall has to be the desire to be faithful to God which places a high premium on abiding by His Word. If there is the reverent attitude that we will not exceed what is written, which is rooted in our love and faith towards the Father, then the teaching of Balaam and the teaching of Jezebel (Rev. 2) will be checked. The Word of God is the firewall that protects the church against false teaching.
As the Elders at Ephesus were commended to the Word of God (Acts 20:32) to be armed against the wolves in sheep’s’ clothing, likewise today we need to pay closer attention to what God says about being saved, true worship, and godly living. It is the firewall.
When it comes to worship, the church is to be united in the assembly and not divided. The words “do not exceed what is written” are helpful to this end, 1 Cor. 4:6. The orderliness and edifying nature of worship as described in 1 Cor. 14 when people are singing, praying, and preaching the Word all call for us to follow the Bible and add nothing to it.
This is why we sing songs and do not add the artificial noise of musical instruments. The early church avoided their use like the plague. The early church, and all who claimed to follow Christ Jesus, only sang until the Catholics introduced them hundreds and hundreds of years later. In the church of Christ today we only sing. We don’t seek to entertain weak and unspiritual men. If a person is of the mind to seek God, he or she will delight in the spiritual songs of the church.
And in the church we teach salvation by grace through faith. Grace is what God did through Jesus and it is what God does to wash a sinner’s soul clean. Now though God provides the means of escape to all men, and since we know that most will not accept the invitation from God, then we know that the salvation is only given by God to those who have an active, lively, and obedient faith, Eph 2:8,9. This means that upon hearing the Gospel, the person reflects on his or her sin, repents, turns to God, acknowledges that Jesus is the Son of God, and then gets baptized down into the water for the sins to be washed away by His blood. This is the salvation we read about in the Word of God. If we do not exceed what is written, this is what we will do. See Acts 2:38; 22:16; Rom 6:3-5; Gal. 3:26,27; Col 2:12,13; 1 Pt 3:21.
If the church will abide in God’s Word, we shall be pure and pleasing to God.