Can a Christian Err From The Truth and Lose His Soul's Salvation?

James’ epistle was written to those who had “the faith of our Lord Jesus Christ” (James 2:1); who could pray the effectual fervent prayer of a righteous man” (5:16); and whose faith was being tried” (1:2, 3). To the Jewish Christians “scattered abroad” (1:1) he wrote:

James 5:19-20

Brethren, if any of you do err from the truth, and one convert him;

Let him know, that he which converteth the sinner from the error of his way shall save a soul from death, and shall hide a multitude of sins.

KJV

James shows here that a brother in Christ, a child of God, can err from the truth, become a sinner and need conversion “from the error of his way.”  When converted his soul is saved from death.  If he is not converted, then his soul will not be saved from death.

This is speaking of the “second death” (Rev. 21:8), not physical death, for all die physically, both evil and righteous (1 Cor. 15:22; Heb. 9:27).  Even Jesus who “did no sin” died physically.

James teaches us that Error can cost us our salvation.  It is of paramount importance that we as Christians know the Truth of God's Word and obey it.

2 Tim 2:15
Study to shew thyself approved unto God, a workman that needeth not to be ashamed, rightly dividing the word of truth.
KJV

Additional studies relating to the preservation of our salvation:

Was Timothy "Once Saved, Always Saved"?
 

A Believer can become an Unbeliever.