The following was taken from gospelcom.net. The full article can be read here.

In discussing the relevance of doctrine, I mentioned that a person's salvation can depend to some extent on doctrinal understanding. Since this point is so often contested in our day, it deserves closer attention.

Almost everybody who acknowledges Jesus Christ in some way will agree that those who completely and explicitly reject Jesus Christ are lost. Many people find it difficult, however, to believe that some might sincerely think themselves to be following Jesus Christ and yet, due to heretical belief, be lost. Jesus Himself promised, "Seek, and you shall find" (Matt. 7:7); should not those who seek for Christ find Him? And do not many sincere members of groups which evangelicals label heretical truly want to find Christ? They may read the Bible more studiously than many an evangelical church member; they may express an ardent desire to know God and obey Him; they may zealously proclaim the message of Christ as they have been taught it. Are they not, therefore, seeking Christ, and will they not, then, in accordance with His promise, find Christ? And if so, how can salvation depend on doctrinal beliefs?

These questions may be answered by keeping the following biblical principles in mind.

Not everyone who acknowledges Jesus as Lord will be saved. This follows directly from Jesus' own words in Matthew 7:21: Simply acknowledging that Jesus is Lord does not guarantee a person's salvation. The acknowledgment might be mere lip service, as demonstrated by refusal to obey Him as Lord (Luke 6:46). Or someone might call Jesus "Lord" and not mean the same thing as what the Bible means by it. This leads me to a second principle.

Many who claim to acknowledge Jesus actually believe in "another Jesus," and are either deceived or deceiving. This follows directly from 2 Corinthians 11:4. Many who speak of faith in "Jesus" have an understanding of who and what Jesus is that differs so much from reality that in truth they do not have faith in the real Jesus at all. If a person thought Buddha was another name for Moses, we would not normally consider him a Buddhist, no matter how piously and moralistically he lived out his belief in "Buddha. " Similarly, someone who denies the biblical view of Christ should not be identified as a Christian, no matter how religiously he follows his belief.

Some people who believe in "another Jesus" are no doubt insincere, and Paul warns of "deceitful workers who disguise themselves as apostles of Christ" (2 Cor. 11:13). I like to think the best of people, even people with whom I have serious disagreements. But I have become acquainted with a few persons about whom I have had to conclude, reluctantly, that they are simply liars. These people know on a conscious level that the message they proclaim is false.

On the other hand, some people, even members of Christian churches, can be "led astray" (2 Cor. 11:3b) by such deceivers. Thus, it is possible for sincere people, even people who were part of the fellowship of true Christians, to be deceived into following "another Jesus." Not that such people are perfectly innocent — rather, they are like Eve who, though deceived by the serpent (2 Cor. 11:3a), was guilty of sin and held accountable by God (Gen. 3:1-6, 13-16).

Those who are zealous in religious matters are not necessarily saved. In Romans 10:2 Paul says of his Jewish brethren who rejected Jesus, "They have a zeal for God, but not in accordance with knowledge." Zeal, of course, implies sincerity — that is, the mental state of believing that what one is promoting is based on truth. The Jews who rejected Jesus were for the most part zealous, and therefore sincere in this sense — but they were still lost (Rom. 9:1-3; 10:1). Their zeal was, in particular, for a right standing with God — but they sought it on the basis of their own works, as if salvation was by works, rather than receiving the righteousness which was available in Christ through faith (Rom. 9:30-10:4).

Matthew 23:15 addresses zeal of another kind — zeal in seeking converts. The Pharisees were extremely zealous in missionary work, but all they succeeded in doing was leading more people into their error. Zeal in witnessing or evangelizing does not indicate that a religious group is God's people.

No human being truly seeks for God unless God's Spirit draws that person; therefore, those that appear to seek for God but do not come in God's way are not seeking for God at all. In Romans 3:11 Paul quotes Psalm 14:2 to the effect that "there is none who seeks for God." Sin has so perverted the desires of all human beings that none of us, by our own natural wishes, is looking for God. This is because "the mind set on the flesh is hostile toward God" (Rom. 8:7). Of course, some people do seek for God, otherwise God would not call upon us to seek Him (Isa. 55:6, etc.). But when people seek God, it is only because God has first "sought" them and drawn them toward Him by His grace (Luke 19:10; John 6:44; 15:16).

When people therefore appear to be "seeking God" — when they study the Bible (2 Pet. 3:16), attend meetings, pray, change their lifestyles, attempt to obey the commandments, even speak of their love for God and Christ — yet persist in worshipping a false God, or honoring a false Christ, or following a false gospel (Gal. 1:7-9; 2 Cor. 11:4), we must conclude that they were not really seeking God. Rather, they may have been seeking spiritual power, or security, or peace of mind, or warm relationships, or knowledge, or excitement, or anything other than simply God. And in saying this, I am not claiming that all genuine Christians on the other hand have sought purely and simply after God. No, our testimony as Christians must be that we were also following our own divergent path when God sought us, stopped us in our way, and led us up a new and narrow path leading to salvation in Jesus Christ (Matt. 7:13).

Anyone who truly desires to know the truth about God and His way of salvation above all else can and will be saved. This is the other side of the coin from the previous point. Jesus promised that "the one who comes to Me I will certainly not cast out" (John 6:37). However, we must come to the true Jesus on His terms. Judas came to the true Jesus, at least outwardly (actually, Judas did not know who Jesus really was), but he did not come on Jesus' terms and was consequently lost (John 17:12). The cost of abandoning heresy is usually great — the loss of friends, the embarrassment of admitting error, the threat of the heretical teachers that all who leave their teaching will be lost. But salvation is available for anyone who by God's grace puts truth (and the One who is truth) above these things.