Halliday & Matthiessen (2014: 27):
… there are not two separate objects, language as system and language as a set of texts. The relationship between the two is analogous to that between the weather and the climate (cf. Halliday, 1992a). Climate and weather are not two different phenomena; rather, they are the same phenomenon seen from different standpoints of the observer. What we call ‘climate’ is weather seen from a greater depth of time – it is what is instantiated in the form of weather. The weather is the text: it is what goes on around us all the time, impacting on, and sometimes disturbing, our daily lives. The climate is the system, the potential that underlies these variable effects.