We have made it as a reminder and a provision for the travellers at the desert.
‘Made it as a reminder’ means the believers should think that if there is no fire, how difficult life in this world would be, and that they have to become more and more grateful to the Donor of all these facilities on the earth. At the same time, the disbelievers, by seeing the fire, may become fearful about the severe heat of the fire in the Hereafter, which is promised for the disbelievers, and may lead a heedful life here. Since in the olden days the fuels for kindling the fire, such as kerosene, coal, gas, electricity, etc., were not available as nowadays for mankind, especially to the dwellers of the deserts, they depended only on trees for kindling the fire. That is why it is mentioned in this verse, particularly about the dwellers of the deserts. See explanation 2: 24; and 36: 80.