Are we allowed to receive those who preach against the traditional beliefs of God's Church? What about their new doctrines?
We are not supposed to believe in any gospel (doctrine) at variance with what we have received from Apostolic times. "I marvel that you are turning away so soon ... to a different gospel... there are some who trouble you and want to pervert the gospel of Christ. But even if we, or an angel from heaven preach any other gospel to you than that we have preached to you, let him be accursed" (Gal. 1 :6-10). Gospel originated in and for the Church by the work of the Spirit. Hence Church is the official interpreter of the Word of God. Peter cautions against any misinterpretation of Paul's epistles. There is a chance that the untaught and unstable twist the Word of God to their destruction (2 Pet. 3:16). Therefore the believers must expect such misinterpretations (Cf. V .17) .In the introduction to his first epistle, John says, "That which was from the beginning, which we have looked upon, and our hands have handled concerning the word of life. we declare to you" (1 John 1:1-4). In his second letter, John cautions against false teachers. "For many deceivers have gone out into the world who do not confess Jesus Christ as coming in flesh. This is a deceiver and Anti Christ" (1:7). "Do not receive him into your house nor greet him, for he who greets him, shares in his evil deeds (VV 8-11). Jude also warns that sensual persons who are not led by Holy Spirit would cause divisions in the Church (Cf. 1: 17-23). Jesus himself has cautioned against such deceivers (Cf. Mt. 24:4-5). "Many false prophets will rise up and deceive many" (V. 11). They may show great signs and wonders so as to deceive even the elect (V 24) but do not believe them (VV. 25-26). Paul admonishes the elders of the church to protect their sheep from the wolves (Acts 20:28-30). Therefore take heed to yourselves and to all the flock, among which the Holy Spirit has made you overseers, to shepherd the Church of God which He purchased with his own blood" (V 30). Hence the authorities must be vigilant against such false teachers, and the faithful shall never entertain them.