Hi Stones,
I don't really think that the Lord is talking about those who might believe for awhile and seem to fall away and return again. There's always forgiveness offered to those who repent.
Here's the explanation of the parable in Matthew.
Hear then the parable of the sower. When anyone hears the word of the kingdom and does not understand it, the evil one comes and snatches away what has been sown in his heart. This is the one on whom seed was sown beside the road. The one on whom seed was sown on the rocky places, this is the man who hears the word and immediately receives it with joy; yet he has no firm root in himself, but is only temporary, and when affliction or persecution arises because of the word, immediately he falls away. And the one on whom seed was sown among the thorns, this is the man who hears the word, and the worry of the world and the deceitfulness of wealth choke the word, and it becomes unfruitful. And the one on whom seed was sown on the good soil, this is the man who hears the word and understands it; who indeed bears fruit and brings forth, some a hundredfold, some sixty, and some thirty.”
The parable is actually talking about the heart of 4 types of people who accept the truth of the gospel.
The first one is the soil by the side of the road and as soon as he hears the gospel, the seed is snatched away by satan; this person is shallow.
The second one has rocky soil. He hears the gospel and receives it with joy, but he has no deep root; when persecution hits or affliction comes upon him because of the lack of the deep root he leaves the faith.
The third soil is thorny, but the worry of the world and the deceitfulness of wealth chokes the word and it becomes unfruitful. This soil produces no fruit at all.
Only the good soil hears the word, understands it and bears fruit.
Those that waver, but in the end repent and return to the Lord are the good soil just as much as the one who continues faithfully all his life.
I'm sure some will disagree, but that's what I believe this parable is teaching. Only those with good soil can receive the gospel truth and continue on in the faith.