Meaning, Allah (swt) will inflict him with a severe punishment without any relaxation. The Prophet (saws) described this statement saying:

“As-Sa’ud is a mountain of fire, a disbeliever will be rised upon it for seventy autumns, and them similarly he will fall down it, forever.”[1]

In another verse, Allah (saw) says:

 وَمَن يُعْرِضْ عَن ذِكْرِ رَبِّهِ يَسْلُكْهُ عَذَابًا صَعَدًا

(And whoever turns away from the remembrance of his Lord He will put into arduous punishment.) (Al-Jinn: 17)

The disbelievers will suffer the torment of climbing the mountain of fire that they can climb with great difficulty.

[1] Sunan at-Tirmidhi, Chapters of Tafsir Al-Quran, hadith No. 3326.