When studying Salvation, it is important to consider all scripture before concluding whether a "Christian" can lose or forfeit their salvation. It is scripturally clear that God has completed the sacrifice for which salvation is granted, for all of God's work is perfect and complete.
But, the question still arises whether Christians can lose their salvation? It is blasphemy to abuse the sacrifice of the cross, and belittle the grace for which we all have been saved by continuing to live in self-indulgence and sin. For, a "genuine" Christian, resembles the work of God's hands, His mercy, His love, His humility, His character, His likeness, His image, and of course His Spirit. When considering this issue, we must understand fully that a "Christian" is one who believes in his heart and confesses with his mouth that Jesus Christ is Lord (governor, ruler, king) and that he resurrected from the dead (Romans 8). This confession is not simply a dictation, or a verbal declaration, for even demons, will confess this, but an internal working of faith which has been proportioned by God, working through the circumcised heart of a believer.
If in truth, "Jesus Faith", has settled within the heart of a believer, God and angels rejoice and the Holy Spirit immerses the believer in his truth. This eternal work shall not be damned by doctrine, but fulfilled by the truth. For a Christian, who has been filled with the Holy Spirit, will bear the fruits of the Spirit. This is denoted in the word "fellow" or "fellowship". Throughout scripture, we can see that God calls us "fellow workers", or that we may have "fellowship" with him or other believers. This word is rich in depicting the importance of remaining in Christ, for God sees our divine relationship, through the scope of us remaining in fellowship with him.
For a "true" Christian is one who has forfeited his worldly relationship, for a divine one. This, in turn, will assure and secure his eternal reward. You can not have true fellowship with God, and still, come out looking and acting like the world. But, of course, this is finally revealed through time, and God will certainly judge the thoughts of the heart.
Food for thought, What is the difference between a sheep and a goat?
31 “When the Son of Man comes in his glory, and all the angels with him, he will sit on his glorious throne. 32 All the nations will be gathered before him, and he will separate the people one from another as a shepherd separates the sheep from the goats. 33 He will put the sheep on his right and the goats on his left.
34 “Then the King will say to those on his right, ‘Come, you who are blessed by my Father; take your inheritance, the kingdom prepared for you since the creation of the world. 35 For I was hungry and you gave me something to eat, I was thirsty and you gave me something to drink, I was a stranger and you invited me in, 36 I needed clothes and you clothed me, I was sick and you looked after me, I was in prison and you came to visit me.’
37 “Then the righteous will answer him, ‘Lord, when did we see you hungry and feed you, or thirsty and give you something to drink? 38 When did we see you a stranger and invite you in, or needing clothes and clothe you? 39 When did we see you sick or in prison and go to visit you?’
40 “The King will reply, ‘Truly I tell you, whatever you did for one of the least of these brothers and sisters of mine, you did for me.’
41 “Then he will say to those on his left, ‘Depart from me, you who are cursed, into the eternal fire prepared for the devil and his angels. 42 For I was hungry and you gave me nothing to eat, I was thirsty and you gave me nothing to drink, 43 I was a stranger and you did not invite me in, I needed clothes and you did not clothe me, I was sick and in prison and you did not look after me.’
44 “They also will answer, ‘Lord, when did we see you hungry or thirsty or a stranger or needing clothes or sick or in prison, and did not help you?’
45 “He will reply, ‘Truly I tell you, whatever you did not do for one of the least of these, you did not do for me.’
46 “Then they will go away to eternal punishment, but the righteous to eternal life.”