What does Mark 8:35 mean?

"Loses his life" refers to a Semitic phrase "to trifle away one's life." It means the loss is caused by foolish actions, not accident or happenstance. "Life" is from the Greek root word psuche. It means breath of life, but can also refer to one's soul.

Some are called to sacrifice their lives for Jesus and the gospel. According to legend, many of the twelve disciples were martyred. We are to accept that martyrdom is a possibility, but not seek it out (Matthew 10:23). God will honor martyrs. When Stephen is being stoned, he sees Jesus standing at the right hand of God (Acts 7:56). And martyrs will be honored during the Tribulation (Revelation 20:4). Persecution, if not death, is something all Christ-followers should expect (2 Timothy 3:12).

But we can also lose our souls by trying to save them. The Bible is clear that salvation is through grace, by faith. We are completely incapable of doing the work that would save our souls. To try is to reject Jesus' offer of salvation, and without Jesus, our souls are forfeit (Ephesians 2:8–9; John 3:16–18).

The life of a Christ-follower is filled with little "deaths" as well. Some kind of persecution is likely (John 15:20; 2 Timothy 3:12). If other family members are not saved, we can expect a rift in relationships (Matthew 10:35–36). But the Bible promises compensation. Jesus calls those who listen to Him His family (Mark 3:33–35). And God will give rewards in heaven to those who are persecuted on Jesus' account (Matthew 5:12).