بَلْ سَوَّلَتْ لَكُمْ أَنْفُسُكُمْ أَمْرًا
Rather, your own selves have made a matter seem appealing to you.
In 12:18, bal redirects the discussion away from the presented report toward a corrective account: their own selves have made some matter attractive to them. The particle marks a substantive difference, not merely a smooth joining of equivalent clauses.
A rhetorical reading need not invent the full sequence of events that the verse does not state. The grounded point is the turn from a claim toward an alternative explanation.