Allah tells us how the rich man's believing companion replied to him, warning and rebuking him for his disbelief in Allah and his letting himself be deceived.

This is a denunciation, pointing out the seriousness of his rejection of his Lord Who created and formed man out of dust - that is, Adam - then made his offspring from despised liquid, as Allah says:

{How can you disbelieve in Allah? Seeing that you were dead and He gave you life.} [2:28]
meaning, how can you reject your Lord and His clear signs to you, which every one recognizes in himself, for there is no one among mankind who does not know that he was nothing, then he came to be, and his existence is not due to himself or any other creature. He knows that his existence is due to his Creator, beside Whom there is no other god, the Creator of all things.

So the believer said:

meaning, 'I do not say what you say; rather I acknowledge the Oneness and Lordship of Allah,'

meaning, He is Allah, the One Who is to be worshipped Alone, with no partner or associate.

Then he said:

Here he was urging and encouraging him to say that, as if he was saying, "When you entered your garden and looked at it and liked it, why would'nt you praise Allah for the blessings He gave you and the wealth and children that He has given to you and not to others? Why did you not say 'That which Allah wills! There is no power but with Allah!'" One of the Salaf said, "Whoever is delighted with something in his circumstances or his wealth or his children, let him say, 'That which Allah wills! There is no power but with Allah!'" This is based on this Ayah. It was reported in the Sahih from Abu Musa that the Messenger of Allah said:

"Shall I not tell you about some of the treasure of Paradise? La hawla wa la quwwata illa billah (There is no power or might but with Allah)."

in the Hereafter

{and will send on it} on your garden in this world, which you think will never come to an end or cease to be,

Ibn 'Abbas, Ad-Dahhak and Qatadah said - and Malik narrated that Az-Zuhri said - a punishment from heaven. The apparent meaning is that it is a mighty rain which would disrupt his garden and uproot its plants and trees. As he said:

{then it will be as a barren slippery earth.} meaning, smooth mud in which one cannot get a foothold. Ibn 'Abbas said, "Like land without vegetation, where nothing grows."

means, it disappears into the earth, which is the opposite of flowing water that seeks the surface of the earth. So Gha'ir is to go lower, as Allah says:

{Say: "Tell me! If your water were Ghawran, who then can supply you with flowing water?"} [67:30]

meaning, water that flows in all directions. And here Allah says:

Ghawr is from the same root as Gha'ir and has a similar meaning, but is more intensive.