This is one that can go back and forth depending on the understanding of eternal security.
Too many times legalism teaches that one falls from grace when one fails to fulfill the legalistic teachings of their individual group.
The fact is the primary falling from grace came when one returned to the legalism of the keeping of the law and oricles from which they had come out of.
Hence is the parridox, yes one can loose ones relationship with God. When you trust more in your own efforts than grace and the work of the cross. But this comes from an improper veiw of what salvation truly is.
I don't believe salvation is the striving in this life to gain eternity. Salvation is being reconciled to God through Christ in this present life. As long as one walks after the spirit in this life in communion with God they are eternaly saved.
Brake that communion, and what do you have? Nothing. We are told very explicitly what things will not enter the kingdom of God.
Gal 5:19 Now the works of the flesh are manifest, which are these; Adultery, fornication, uncleanness, lasciviousness,
Gal 5:20 Idolatry, witchcraft, hatred, variance, emulations, wrath, strife, seditions, heresies,
Gal 5:21 Envyings, murders, drunkenness, revellings, and such like: of the which I tell you before, as I have also told you in time past, that they which do such things shall not inherit the kingdom of God.
Here is where I see the problem, too many times we dwell on sin or what we think is sin. When Paul tells us that if we walk after the spirit we will not lust after the flesh.
Gal 5:16 This I say then, Walk in the Spirit, and ye shall not fulfil the lust of the flesh.
Gal 5:17 For the flesh lusteth against the Spirit, and the Spirit against the flesh: and these are contrary the one to the other: so that ye cannot do the things that ye would.
Gal 5:18 But if ye be led of the Spirit, ye are not under the law.
How shall this be?
Gal 5:14 For all the law is fulfilled in one word, even in this; Thou shalt love thy neighbour as thyself.
Much more can be said, but I beleive the bottom line is that we can rest in the security of Grace knowing our salvation is sure as long as we walk after the spirit. By this our salvation is sure.
One cannot walk after the flesh and have the spirit, walk after the spirit and you cannot walk after the flesh. They that have not the spirit are none of his.