An old proverb goes: “God defend me from my friends; from my enemies I can defend myself.” Julius Caesar’s dying words, at least in Shakespeare’s play, were “et tu Brute?” Brutus was one of the senators who stabbed him to death, in an attempt to overthrow him. Politicians are well aware of attacks from their opposition, but the ones that cause the most harm are sometimes from within their ranks. Similarly, in 1 John 4:1-6 the Apostle John tells us to beware of those who appear to be from within the Church, but who are really opposed to the truth of Christ. He also tells us how to spot the difference. While Christians are well aware of opponents, such as those who attempt to marginalise Christianity from public life in the West, or the new atheism that has arisen recently, we are often much less on our guard against those from within who are opposed to the gospel of Jesus Christ. There are various individuals, or loosely connected groups of individuals, who have a problem with one aspect of Christianity or another. Secondary matters should not divide us, but when primary matters are opposed, we have to react. For example, when the cross of Calvary is not about resolving our sin problem before God, but is just an extravagant example of God’s love for us. John tells us to be careful what we believe – not to be gullible and accept everything without testing it according to the test of those who are eye witnesses of Jesus and his glory. He shows that false teachers leave and return to their natural home, the world, because they never belonged to the Church anyway. People listen either to the Word or the World. We must believe and uphold the gospel of Jesus Christ, as the test of orthodoxy. And he encourages believers to depend on the Holy Spirit within them to guide them into truth, because he is greater than the spirit of untruth in the world. The Bible needs to be the truth we stand on, and not public opinion or new teachings that are not in line with God’s Word. This is more of a live issue for some than others, such as the debates with the Anglican Church worldwide as to whether their leadership is standing squarely on the Bible as it’s source of authority, or not. John wants God’s children to have joy and assurance in their salvation. His guidance to be careful about what we listen to can prevent us letting opponents from within the broad category of ‘Christianity’ do damage to the cause of Christ, and hurt God’s children.