Tafseer Ibn Kathir of AL KAHFI [7]

إِنَّا جَعَلْنَا مَا عَلَى الْأَرْضِ زِينَةً لَّهَا لِنَبْلُوَهُمْ أَيُّهُمْ أَحْسَنُ عَمَلًا

Indeed, We have made that which is on the earth adornment for it that We may test them [as to] which of them is best in deed.