Though they acknowledge many truths found in the Bible, they deny many others.
1. They believe the Bible is the infallible and inerrant word of God. (The Christadelphians: What They Believe and Preach, p. 82)
2. They teach there is only one God. (Isaiah 43-45)
3. They teach that Jesus had a sin nature (What They Believe, p. 74)
4. They teach that Jesus needed to save himself, before he could save us. (Christadelphian Answers, p. 24)
5. They teach that Jesus will return and set up his kingdom on earth. (What They Believe , p. 268)
6. They believe that there has been an apostasy and that Christianity is a false religious system. (A tract titled “Christendom Astray Since the Apostolic Age, Detroit Christadelphian Book Supply)
7. They believe annihilation of the wicked. (What They Believe, p. 187).
8. They believe that baptism is necessary for salvation. (What They Believe , p. 71,72, 207-210)
9. They believe that it is possible to lose one’s salvation. (What They Believe , p. 212)
10. They deny the doctrine of the Trinity. (What They Believe, p. 84-87)
11. They deny that Jesus is God in flesh. (Answers, p. 22)
12. They deny that Jesus existed prior to his incarnation. (What They Believe , p. 85,86)
13. They deny the personhood and deity of the Holy Spirit. (What They Believe , p. 115)
14. They deny the substitutionary atonement of Christ. (Answers, p. 25; What They Believe, p. 71)
15. They deny salvation by grace through faith alone. (What they Believe, p. 204)
16. They deny immortality of the soul. (What They Believe , p. 17).
17. They deny that a person exists after death. (What They Believe, p. 17)
18. They deny the existence of hell and eternal punishment. (What They Believe, p. 188-189)
19. They deny the existence of the fallen angel Lucifer as the devil. (Answers, p. 100)
As you can see, the Christadelphians deny some essential doctrines of Christianity; namely, the deity of Jesus and salvation by grace.
Like so many other cult groups that claim to be the restored truth, they have their own interpretations of the Bible that deviate greatly from orthodox Christianity.