This aya means: the disbelievers and idolaters considered the Quran like the spiky thorn, and the Quran was to them like the spiky thorn: i.e. they contracted from it extremely.
In other words, God misguided them to the extent that the Quran to them is like the spiky thorn;
and they disgust from the belief in God alone; they in fact are the disbelievers in the next afterlife that disgust when God alone is mentioned: that He alone deseves to be worshipped exclusively.
(When God, Alone is mentioned [that He alone deserves to be worshipped], the hearts of those who believe not in the afterlife are filled with disgust;
but when those apart from Him are mentioned [with praise], behold, they rejoice.)
The above between brackets is the explanation, by Mohammed-Ali Hassan, of the Quran 39: 45
وَإِذَا ذُكِرَ اللَّهُ وَحْدَهُ اشْمَأَزَّتْ قُلُوبُ الَّذِينَ لَا يُؤْمِنُونَ بِالْآخِرَةِ وَإِذَا ذُكِرَ الَّذِينَ مِن دُونِهِ إِذَا هُمْ يَسْتَبْشِرُونَ