ABC:John 17

Verse 20 (Christian Unity)
Patheos' Bob Seidensticker claims there is a contradiction here and makes the following comments (italicized):

All Christians are united in what they believe about Jesus (right?) John 17:20-23 ¶ Neither pray I for these alone, but for them also which shall believe on me through their word; That they all may be one; as thou, Father, art in me, and I in thee, that they also may be one in us: that the world may believe that thou hast sent me. And the glory which thou gavest me I have given them; that they may be one, even as we are one: I in them, and thou in me, that they may be made perfect in one; and that the world may know that thou hast sent me, and hast loved them, as thou hast loved me. 1 Corinthians 1:10 ¶ Now I beseech you, brethren, by the name of our Lord Jesus Christ, that ye all speak the same thing, and that there be no divisions among you; but that ye be perfectly joined together in the same mind and in the same judgment. That’s a nice thought, but has any prayer failed more spectacularly? Christianity is more than just Roman Catholics and Baptists and Methodists and maybe a few more—there are now 45,000 denominations, and Christianity is fragmenting at a rate of two new denominations per day. (h/t commenter Greg G.)

The fact that Christians are one with God the Father, Jesus the Son of God, and the Holy Spirit, as well as with each other, hardly means that all Christians have the exact same beliefs. For more on oneness, see the Trinity.

That 1 Corinthians 1:10 is quoted here like this displays a blatant ignoring of context on the part of the critic, as the whole reason Paul is writing is to urge the Corinthian Church NOT to be divided on their beliefs. In the very next verses (11-13) Paul states that the Corinthians are divided: "For it hath been declared unto me of you, my brethren, by them which are of the house of Chloe, that there are contentions among you. Now this I say, that every one of you saith, I am of Paul; and I of Apollos; and I of Cephas; and I of Christ. Is Christ divided? was Paul crucified for you? or were ye baptized in the name of Paul?"

The division of the early Church into factions was occurring even in Paul's time, which is why he was urging Christians to instead unite with one another. However, Jesus and Paul both warned that there would be false Christians who would claim to be God's people. (Matthew 7:22-23; 2 Corinthians 11:13; Matthew 24:24; Galatians 1:7; Acts 20:29-30) For this reason, Jesus advised that we will know who His people are, not by them claiming to be Christians, but by the good deeds they will perform. (Matthew 7:16-21) John similarly urges us to test spirits to see whether they are of God since there are many false prophets. (1 John 4:1-3)