Through his death and resurrection, Jesus opened the way to God and paid the penalty for our sins. As a result, he can promise us that if we have faith in him, our sins are forgiven and salvation is guaranteed. The promise that Jesus makes in Mark 8:35, that those who lose their life for the sake of the gospel will save it, is a promise we can trust. Whoever comes to true faith in Jesus Christ, whoever denies himself and takes up his cross, such a person will save his life.
In calling his disciples and the crowd to a life of self-denial and cross bearing, Jesus is not asking them (and us) to do anything that he has not done himself. He’s not sitting in heaven bossing us around from a distance. He is our Shepherd, leading us from the front (Psalm 23:1–6, Mark 6:34). He is our Shepherd who has given himself to save his sheep (Mark 10:45, John 10:1–30), who knows about our suffering and temptations (Hebrews 4:15), and who calls us to follow him with the assurance that he has provided salvation for us, and he will continue to care for us.
31 And he began to teach them that the Son of Man must suffer many things and be rejected by the elders and the chief priests and the scribes and be killed, and after three days rise again.