What is the consequence of rejecting the gospel?
The consequence of rejecting the gospel is being placed into the Lake of Fire for the lost. This stands in contrast to becoming a believer and experiencing the baptism of the Spirit. The choice is between accepting the Spirit's baptism or rejecting it and facing the Lake of Fire.
Les teaches that the choice is clear: either become a believer and experience the baptism of the Spirit, or reject it and one day be placed into the Lake of Fire for the lost. He grounds this consequence in Matthew 3:12. The surrounding passage discusses the baptism of Jesus, where all three members of the Trinity are present, but the key contrast remains between accepting the Spirit's baptism and rejecting it, which leads to the Lake of Fire.
Whose fan is in his hand, and he will throughly purge his floor, and gather his wheat into the garner; but he will burn up the chaff with unquenchable fire.