Growing up I was taught that once you were saved, you were saved forever and could not lose your salvation, but over the years I’ve found too many verses that don’t seem to support this view.
I agree a lot of verses do talk about pretenders, but there are a few more that seem to talk about people rejecting the Spirit after having received it. Here is an example from Luke 8:
He spoke by way of a parable: “The sower went out to sow his seed; and as he sowed, some fell beside the road, and it was trampled under foot and the birds of the air ate it up. Other seed fell on rocky soil, and as soon as it grew up, it withered away, because it had no moisture. Other seed fell among the thorns; and the thorns grew up with it and choked it out. Other seed fell into the good soil, and grew up, and produced a crop a hundred times as great.” As He said these things, He would call out, “He who has ears to hear, let him hear.”
His disciples began questioning Him as to what this parable meant. And He said, “To you it has been granted to know the mysteries of the kingdom of God, but to the rest it is in parables, so that ‘seeing they may not see, and hearing they may not understand’.
“Now the parable is this: the seed is the word of God. Those beside the road are those who have heard; then the devil comes and takes away the word from their heart, so that they will not believe and be saved. Those on the rocky soil are those who, when they hear, receive the word with joy; and these have no firm root; they believe for a while, and in time of temptation fall away. The seed which fell among the thorns, these are the ones who have heard, and as they go on their way they are choked with worries and riches and pleasures of this life, and bring no fruit to maturity. But the seed in the good soil, these are the ones who have heard the word in an honest and good heart, and hold it fast, and bear fruit with perseverance.
Remember, when Jesus is talking about the Word, he does not mean scripture. He is talking about the active, immediate prompting of the Holy Spirit–the voice of God. He is talking about himself. I think this is also what Hebrews 3 is talking about.
Now Moses was faithful in all His house as a servant, for a testimony of those things which were to be spoken later; but Christ was faithful as a Son over His house—whose house we are, if we hold fast our confidence and the boast of our hope firm until the end.
Take care, brethren, that there not be in any one of you an evil, unbelieving heart that falls away from the living God. But encourage one another day after day, as long as it is still called “Today,” so that none of you will be hardened by the deceitfulness of sin. For we have become partakers of Christ, if we hold fast the beginning of our assurance firm until the end, while it is said,
“TODAY IF YOU HEAR HIS VOICE,
DO NOT HARDEN YOUR HEARTS, AS WHEN THEY PROVOKED ME.”
For who provoked Him when they had heard? Indeed, did not all those who came out of Egypt led by Moses? And with whom was He angry for forty years? Was it not with those who sinned, whose bodies fell in the wilderness? And to whom did He swear that they would not enter His rest, but to those who were disobedient? So we see that they were not able to enter because of unbelief.
(Hebrews 3:5-6, 12-19)
I understand this is a hard truth. But God seeks us wholly. He asks us for our love. We can be angry, sad, frustrated, confused, and everything else, but at the end of the day there must be commitment from our end.
Hebrews 3 twice says to hold fast until the end. And as Jesus says, we must hold him fast and bear fruit with perseverance.