This would be true if we were talking about the deity of Christ, the Triune nature of God, justification by faith alone or salvation by grace alone, the physical return of Christ for the regeneration of creation, but we're talk a secondary issue of eschatology. It's a secondary doctrine, it's not satan's lie, Jesus said no one knows the time, only the Father, the only problem that I see can happen is someone placing a date on His return, like John Hagee did, why is it that a preacher will start teaching only on eschatology and then will set a date, it always seems to happen. We need to teach the word of God, I prefer verse by verse, chapter by chapter and book by book, the whole council of God, not cherry picked verses taken out of context to make the preachers point, not God's. Preaching is the proclamation of the Gospel, once you're saved we don't need the Gospel proclaimed to us, we need to be taught the word so we can grow in the grace and knowledge of our Lord Jesus Christ.
I Corinthians 13:8-12 "Love never ends. As for prophecies, they will pass away; as for tongues, they will cease; as for knowledge, it will pass away.9 For we know in part and we prophesy in part,10 but when the perfect comes, the partial will pass away.11 When I was a child, I spoke like a child, I thought like a child, I reasoned like a child. When I became a man, I gave up childish ways.12 For now we see in a mirror dimly, but then face to face. Now I know in part; then I shall know fully, even as I have been fully known."
Prophecy is in part, we know in part, because we look into a mirror dimly, but when the perfect (Jesus) comes then we will know fully. Pauls not talking about the nature of God, justification, salvation, grace or faith, these thing we can know fully when we are born again, because the Spirit leads in all truth.
John 16:13-14 "When the Spirit of truth comes, he will guide you into all the truth, for he will not speak on his own authority, but whatever he hears he will speak, and he will declare to you the things that are to come. 14 He will glorify me, for he will take what is mine and declare it to you."
Things to come, is that eschatology, maybe, but the disciples seemed to know about the end of the age. So pre-trib, post-trib, mid-trib, pre-millinial, post-millinial or a-millinial if it doesn't effect your doctrine on grace, faith, justification by grace, salvation by faith, the Deity of Christ, His atonement, God's Triune nature, Deity of the Spirit, infallible Scripture in the original manuscripts. Is there more I don't know did I go to far, I don't know.