To answer this question, we must first distinguish eternal salvation and eternal sanctification in Christ from daily Christian spiritual fellowship, practical sanctification, communion with God while on earth, and the connection with God called spirituality.
Those who have once believed in Jesus as God and man, crucified for their sins and resurrected, are eternally saved and sealed by God irrevocably, per Ephesians 1:3-14. This is the biblical definition of salvation, and people who have once believed in Jesus are thereafter forever-saved people. Salvation is a FREE GIFT, with no strings attached whatsoever.
Secondly, now, what you are talking about is whether those who have once believed and are eternally sanctified–are, by faith, living out their identity in the obedience of practical sanctification and practical faith in their new identity, by His grace.
Are they following the Spirit of God and are they -practically-, in daily life, being sanctified by the Holy Spirit of love and grace?
Are their minds being transformed?
Are their souls being transformed?
Are they living in spiritual communion with the living God?
Or are they living carnally and grieving the Spirit of God?
That is the question, not their status as saved Christians.
Salvation, which consists of forgiveness of all sins past, present, and future; a new self in Christ that is perfect; and the irrevocable guarantee of going to Heaven at death, is a free gift.
God, in practical sanctification, however, works through our wills. It takes an effort, for those who live in God’s love, for those who love God, and many are not willing to give that effort, that obedience, they are not willing to rely on God to live a holy and loving life here on Earth.
They are not willing to humbly rely on God, by faith and by His grace, for their new identity in Christ, for divine love, for holy desire and for spiritual energy.
Many are not willing to rest and abide in the Vine, who is Jesus, who is love, in order to produce these fruits.
Many, it seems most, of us saved people are like the saved believers in Corinth, too often living after the sinful flesh instead of after the Spirit.