Wealth is a trust
When the text commands spending, it recalls that the human being is only a trustee of what he owns, and that everything returns to God. Stinginess is then set before the One who is Self-Sufficient.
Sura 57 links these three ideas. First the command, with its reason: "spend from that which He has made you trustees of" (57:7). Then the question: "what is [the matter] with you that you do not spend in the way of God, while to God belongs the inheritance of the heavens and the earth?" (57:10). What one keeps, one does not keep: it will return to its owner.
Finally the stingy: "Those who are stingy and enjoin stinginess upon people. And whoever turns away — indeed God is the Self-Sufficient, the Praiseworthy." (57:24). It is the same pair as in sura 92, where the one who withholds "considers himself self-sufficient" (92:8): the stingy one believes he needs nothing, whereas only God does not (“Seeing oneself self-sufficient, the reverse of purifying oneself”).
The same sura describes the present life as "rivalry in accumulation of goods and children" (57:20), the very words that open sura 102.
In the text
وَأَنفِقُوا۟ مِمَّا جَعَلَكُم مُّسْتَخْلَفِينَ فِيهِوَلِلَّهِ مِيرَٰثُ ٱلسَّمَٰوَٰتِ وَٱلْأَرْضِفَإِنَّ ٱللَّهَ هُوَ ٱلْغَنِىُّ ٱلْحَمِيدُ