This should not be a legitimate question anymore. The only reason it is asked is because of the FENCE they try to teeter on.How do you think it becomes ours?
It becomes "theirs" because they were sitting on their fat butts, eating, drinking and being very merry......And BAM God regenerated them.
And it's our fault for not "getting" what they are truly saying.
And notice......The Lord Jesus Christ is nowhere in their salvation......Just the sovereignty of a god.