A cult is a group that claims that it, and it alone, has the truth about God and offers the only way to salvation. Members reject what Christians have believed for almost 2,000 years, and substitute instead their own beliefs for the clear teachings of the Bible.
Often, they add to the Bible by claiming that the books their founder wrote or "discovered" are from God, and have equal authority to the Bible. In reality, however, those books deny what the Bible says about God or Jesus, or about the way of salvation.
The particular group you mention elsewhere in your letter uses its own "translation" of the Bible, which changes what the Bible actually says at certain key points. The Bible warns that before Christ's return many people "will turn their ears away from the truth and turn aside to myths" (2 Timothy 4:4).
My prayer is that you will turn to Jesus Christ and commit your life to Him. He alone is God's Son, sent from heaven to save us from our sins. When we put our faith and trust in Him, He saves us solely by His grace. Open your heart to Him today.
Then ask God to lead you to a church where Christ is honored and the Bible is taught, and where you can grow spiritually. And pray for this couple, that their eyes may be opened to God's truth and they will put their faith in Christ alone for their salvation.