To illustrate: A farmer cultivates the land. Of course, sunshine and water are necessary; without such he cannot expect any harvest.
وَلكِنْ هَلْ يَجْنِي ٱلْمُزَارِعُ أَيَّ مَحْصُولٍ مَا لَمْ يَعْمَلْ بِكَدٍّ ؟‏ ‏