Is the definition of the spiritually lost someone who is not a christian? According to the bible, Yes! Because it really should be the definition of a non-christian. Spirituality is not exclusive to Christianity by definition. Pay attention
I should have said spiritually dead but being spiritually lost is synonymous with being spiritually dead.
Let me clarify.
According to certain books of the canonized 66 books otherwise known as the bible (Genesis to Revelation) specifically;
Romans 8:9b9b Anyone who does not have the Spirit of Christ does not belong to him.
Meaning he/she is spiritually dead without Christ, carefully read Ephesians 2:1-10 as it explains the spiritual condition of someone who is not in Christ.
Ephesians 4:5
One Lord (Jesus), One faith (his faith/faithfulness), One baptism (of the Holy Spirit)Every other faith apart from faith in Christ or reliance on Christ's faith is futile. Any other Spirit apart from the Holy Spirit gives death not life.
Galatians 2:16
know that a man is not justified by observing the law, but by faith in Jesus Christ. So we, too, have put our faith in Christ Jesus that we may be justified by faith in Christ and not by observing the law, because by observing the law no one will be justified.
Ergo, If Christ the sustainer of life is not your Lord, If Christ the sustainer of life is not your source of faith, If you have not been baptized by the Holy Spirit/ghost you are spiritually lost/dead
The Christian faith is dependent upon what Christ has done for us not on what we can do for ourselves.
HM