We probably tend to think of our time and of our era as an age of unparalleled confusion and disparate voices about what is the truth. After all, there is every version of church and religious organization on every corner of every town with every type of shingle announcing every sort of idea as the center of the truth. Truly, there a lot of loud voices.
Yet the existence of varied and errant voices claiming connection to Christ and the gospel is not new. They were on the scene in the very first decades of the Christian church. Paul had to deal with them, along with his younger disciples and church leaders like Timothy and Titus. This was a task entrusted to Timothy as he took up residential guidance in the church community in Ephesus.
1:1 – Paul, an apostle of Christ Jesus by the command of God our Savior and of Christ Jesus our hope, to Timothy my true son in the faith: Grace, mercy and peace from God the Father and Christ Jesus our Lord.
3 As I urged you when I went into Macedonia, stay there in Ephesus so that you may command certain people not to teach false doctrines any longer 4 or to devote themselves to myths and endless genealogies. Such things promote controversial speculations rather than advancing God’s work—which is by faith. 5 The goal of this command is love, which comes from a pure heart and a good conscience and a sincere faith. 6 Some have departed from these and have turned to meaningless talk. 7 They want to be teachers of the law, but they do not know what they are talking about or what they so confidently affirm.
It is often said about those who teach Christian-related error, that they show up with a book in one hand (Bible) and a book in the other (some extra teaching that explains or expands upon the Word of God, often with equal authority).
The gospel message (the biblical message) is really fairly simple and basic: We are sinners (related to Adam and Eve) and can’t save ourselves in any way. We must trust God in faith – believing in the promise of a coming savior (Old Testament) or the historic work of the Savior Jesus (New Testament) who sacrificially took our place.
Paul and other early church teachers often found themselves contending against various combinations of Jewish or secular ideas that were mixed with the gospel in a way that, at the end of the day, totally perverted the gospel truth. Many times it related to genealogies – either of a Jewish background and connection, or in the case of an error called Gnosticism, sought to explain intermediate beings (called aeons) that were sorta both spiritual and physical. Yes, it’s confusing and murky, which is why Paul said it leads to “controversial speculations” and “meaningless talk.” Imagine what these folks could have done with genealogy.com as a resource!
But wow, they sure sounded good – “what they so confidently affirm.” False teachers do sound good; so do used car salesmen and dealers in gold and silver investing.
Along the way they also promoted some strictures that needed to be followed religiously. But the true faith is not about performing and doing (apart from the overflow of living a life of godliness and love). The true faith is not about law observance; the law (be it the Old Testament) or laws generally are for those who go in wrongful directions …
8 We know that the law is good if one uses it properly. 9 We also know that the law is made not for the righteous but for lawbreakers and rebels, the ungodly and sinful, the unholy and irreligious, for those who kill their fathers or mothers, for murderers, 10 for the sexually immoral, for those practicing homosexuality, for slave traders and liars and perjurers—and for whatever else is contrary to the sound doctrine 11 that conforms to the gospel concerning the glory of the blessed God, which he entrusted to me.
The great purpose of the Law in the Old Testament was to show a person their sin, to demonstrate how they could not ever measure up to God’s holiness. And sensing that deficiency, a person was to seek grace from God in His gracious offers of forgiveness through sacrifice – that either looked forward to the cross, or back at the historic cross event and resurrection of Christ, the final sacrifice.
Is not the gospel message a wonderful thing? Is it not great that we do not have to go through complicated hoops and rituals of secret beliefs to get to a life-saving reality? It is truly awesome to have a simple message of a gracious offer of salvation from one who paid our price, enabling our lives through faith in that truth to be changed, and for us to have a new way of looking at others and the world around us as we serve God in love. It makes one want to just say, “thank you, thank you” for this gift … which is what Paul essentially goes on to say next to Timothy.
Seriously 
“The former preach Christ out of selfish ambition, not sincerely, supposing that they can stir up trouble for me while I am in chains.
But what does it matter? The important thing is that in every way, whether from false motives or true, Christ is preached. And because of this I rejoice. Yes, and I will continue to rejoice,” (Philippieans 1:17-18)
Sometimes people with false motives can do a fairly good job of preaching the gospel and Paul said he could even rejoice over the gospel being preached through these bad guys.
Galatians 4:17 has another class of bad teachers … teachers who are divisive so they can gain more power for themselves. “Those people are zealous to win you over, but for no good. What they want is to alienate you from us, so that you may have zeal for them.”
See also 3 John verses 9 and 10. (It has only one chapter for anyone new to reading scripture references.)
“I wrote to the church, but Diotrephes, who loves to be first, will not welcome us.
So when I come, I will call attention to what he is doing, spreading malicious nonsense about us. Not satisfied with that, he even refuses to welcome other believers. He also stops those who want to do so and puts them out of the church.”
You are right about some people approaching the truth with the Bible in one hand and another book in the other. One example of course is The Book of Mormon.
Seventh Day Adventists (some anyways among them) put a lot of stock in the many books of Ellen G. White.
Each of these groups may develop a certain strength to compensate for their errors. Remember Galatians 4:7 “Those people are zealous to win you over, but for no good. What they want is to alienate you from us, so that you may have zeal for them.”
These groups that are in error often develop a zeal for their teachings and even a zeal for their interpretation of the Bible. Sometimes, we must admit that it is not all bad. While we can argue strongly and rightly against the teachings of the Jehovah Witnesses, they do preach what they believe. They study and rehearse and train to share their teachings. Mormons also train to share their faith. The “zeal” many of them have for their particular organizations are undeniable. Another cultic group that has since disbanded and renamed itself was very small with a very large media presence. The AP news organization upon the death of its leader called the church “fanatically zealous.”
However it is a natural tendency to want to alienate people from others so that they “may have zeal for them.”
It is the case in politics as well as in bad religion. Denigrate others “throw mud” and hope some sticks. Engage in “negative campaigning” and create therefore a belief that the mudthrower is better than the alternative.
“I am the only thing standing between you and the apocalypse” said a politician who was hitting some wealthy folks up for money.
So, let’s be careful to not demonize or disrespect Jehovah Witnesses or Mormons who show up at our door with their message. If we care for them God may use us to reach them. They have some good things that they do very well. We need to respect their strengths … and not try to argue that the rest of Christianity has it “all together” while they are wicked. It might be better to tell them that true Christianity has a humility about it and respects others. Paul respected certain poets who were not of the Jewish tradition.
I’ll quote this whole passage from Acts 17:22-31 because it shows how Paul reached others by showing respect and pointing out sin and error. He wasn’t overly critical nor overly flattering. He was balanced.
” 22 Paul then stood up in the meeting of the Areopagus and said: “People of Athens! I see that in every way you are very religious.
23 For as I walked around and looked carefully at your objects of worship, I even found an altar with this inscription: TO AN UNKNOWN GOD. So you are ignorant of the very thing you worship– and this is what I am going to proclaim to you.
24 “The God who made the world and everything in it is the Lord of heaven and earth and does not live in temples built by human hands.
25 And he is not served by human hands, as if he needed anything. Rather, he himself gives everyone life and breath and everything else.
26 From one man he made all the nations, that they should inhabit the whole earth; and he marked out their appointed times in history and the boundaries of their lands.
27 God did this so that they would seek him and perhaps reach out for him and find him, though he is not far from any one of us.
28 ‘For in him we live and move and have our being.’ As some of your own poets have said, ‘We are his offspring.’
29 “Therefore since we are God’s offspring, we should not think that the divine being is like gold or silver or stone– an image made by human design and skill.
30 In the past God overlooked such ignorance, but now he commands all people everywhere to repent.
31 For he has set a day when he will judge the world with justice by the man he has appointed. He has given proof of this to everyone by raising him from the dead.””