Their sin was stubbornness... Stubbornness after hearing the truth and the evil one snatching it away..
Unbelief in regards to salvation begins with listening to the voice of the devil.
The devil implants the Evil thinking.
“Listen then to what the parable of the sower means:
When anyone hears the message about the kingdom and does not understand it,
the evil one comes and snatches away what was sown in their heart.
This is the seed sown along the path." Matthew 13:18-19
Evil had to do the initial work in unbelief!
Not the sin nature.
Sin will jump in to set up camp if one wishes to
stubbornly continue to refuse the truth that would correct them.
Rebelliousness and STUBBORNNESS
are the sins that lock in the unbelief that the devil planted in their hearts!
For rebellion is as the sin of witchcraft, And stubbornness is as iniquity and idolatry.
Because you have rejected the word of the Lord.” 1 Samuel 15:23
Those sins (rebellion and stubbornness) are what causes the person's unbelief from the Devil to remain intact!
In regards to salvation.. Sin guards and protects what evil first initiated!
With fallen man.... under normal living, the sin nature guards and protects a sin that the sin nature initiated to that person.
Then the sinner will invent ways to justify their wrong stand. Those invented ways are man's own evil invention.
But, with salvation truth? The devil comes and snatches away what was sown in the heart!
It does not say that sin snatches away the gospel.
It says, evil snatched it away!
When anyone hears the message about the kingdom and does not understand it,
the evil one comes and snatches away what was sown in their heart.
It becomes a reenactment of the time when Satan kept his angels filled with lies as to keep them from the Lord!
It takes a while... And, like you pointed out? Demands clarification.
grace and peace ..............