Paul just finished talking about what we shouldn’t do with God’s plan for us which is have meaningless discussions for hours upon hours wasting our time. Now he’s talking about what we need to focus on which is a “pure heart” and a “good conscience” and a “sincere faith”. I don’t have time to do a word study all of these adjectives but on initial read it sounds pretty good to me. All of these things are significant characteristics of the Christian life. With a pure heart, you can be a testimony of God’s redeeming power. With a good conscience, you can speak freely knowing that your sins are put behind you. With sincere faith, people can see that you’re legitimate and they will be drawn to God. I suppose all of these things are so that we can be better witnesses for him.
“Wandered away into vain discussion.” This, on it’s surface, doesn’t sound deadly. It sounds to me like they’re still at least talking in a Christian setting. At least they speaking to one another and not bringing debauchery into the church or anything like that. I even wrote in my Bible, “This doesn’t sound too wrong other than them wanting to be teachers.” Now though, I see the wrong in this. Vain discussions and genealogies are nice but getting stuck looking at charts can be just as proactive as teaching false doctrine because it isn’t accomplishing anything for God’s kingdom. If you aren’t making disciples, then why do it. A well thought out argument, comment, story, or testimony can be used by Christ to win people over to the faith. Speculation and genealogies and charts and graphs are just meaningless and don’t benefit the church. That’s the point Paul is trying to make here and people can spend so much time on meaningless pursuits. We have to be careful of this ourselves.