As this verse illustrates, sin always leads to death, but focusing on the things of the spirit leads to life and peace. We have not simply switched from "death" to "life." We have changed the route from "the road to death" to "the path to life." Continuing on this path is what Christians do. Focusing on the spirit's things, we leave behind the death way.
Whether a believer is carnal or spiritual, eternal life and position are still secured, as the promise of God rests in His faithfulness. In scripture, death is a symbol of separation from God, and for a carnally-minded individual, it represents an estrangement from God. Carnal mindsets cause believers to construct false values and incorrect perceptions of God and then distance themselves from the Lord.
However, thanks to God, we can change the way we think by focusing on Jesus continuously in order to rectify this sad state of affairs. Let us avoid becoming entangled in the world's ideas about God but instead develop the spirit of Christ. Put aside our carnal mindset and develop a mental attitude fixed on Jesus Christ.

Dear Heavenly Father, I know that what I think eventually comes out as my words and actions. Even when I am faithless, You remain faithful to me. My heart should be fixed on Jesus, and my mind should be shaped in a way that honors You. I pray for wisdom and spiritual things to fill my mind. Don't let me lose myself in worldly and sinful things. Let me concentrate on the eternal things in Your presence. 
In Jesus's name I pray. Amen.