Allah (swt) said about the disbeliever: We will drive them into a Fire. Whereas He (swt) said about the believers:

(… سَنُدْخِلُهُمْ جَنَّاتٍ تَجْرِي مِن تَحْتِهَا الْأَنْهَارُ خَالِدِينَ فِيهَا أَبَدًا ۖ لَّهُمْ فِيهَا أَزْوَاجٌ مُّطَهَّرَةٌ …) (…We will admit them to gardens beneath which rivers flow, wherein they abide forever. For them therein are purified spouses,…): The Arabic word of (will) used in both cases differs. The first indicates that there is a time, and the use of the second indicates that it is close, because heaven is always close to the believer, while the unbeliever and the one who practices evil on earth feel that there is a long term, as if death will not knock on his door whereas it is closer to him than his jugular vein.

(garden) is a dense forest of trees that the density of its branches covers underneath. This is the linguistic meaning of the word (garden) in Arabic, so it is a name for something known and existing, and because it is called here for something unseen, Allah (swt) says:

 مَّثَلُ الْجَنَّةِ الَّتِي وُعِدَ الْمُتَّقُونَ

(The example of the Garden) (Al-Baqara: 285)

Meaning, it is as the garden which we know but not exactly the same. The Prophet (saws) said about the Paradise:

“Allah said, ‘I have prepared for My pious worshipers such things as no eye has ever seen, no ear has ever heard of, and nobody has ever thought of.”[1]

It is not as we imagine it with our worldly perceptions that our eyes see and our ears hear and what comes to our minds.

( وَنُدْخِلُهُمْ ظِلًّا ظَلِيلًا … ) (…and We will admit them to deepening shade): This, as well, is unseen matter, Allah (swt) brings it closer to the human mind and what is similar to it in the world.

[1] Sahih Al-Bukhari, Book: The Beginning of Creation, Chapter: The description of Paradise, Hadith No. 3072.