On Unity—To remain divided is sinful! Did not our Lord pray, that they may be one, even as we are one (Jn:17:22)? A chorus of ecumenical voices keep harping the unity tune. What they are saying is, "Christians of all doctrinal shades and beliefs must come together in one visible organization, regardless.... Unite, unite!"
Such teaching is false, reckless and dangerous. Truth alone must determine our alignments. Truth comes before unity. Unity without truth is hazardous. Our Lord's prayer in John 17 must be read in its full context. Look at verse 17: "Sanctify them through thy truth: thy word is truth." Only those sanctified through the Word can be one in Christ. To teach otherwise is to betray the Gospel. (Emphasis added)
Charles H. Spurgeon, The Essence of Separation