What is meant by "Allah withholds and extends"?

Imām Ibn al-Jawzī (d. 597/1201) summarized the scholars' opinions in his book "Zād al-Masīr" as follows:

1. It means that Allah restricts provision for whom He wills and expands it for whom He wills. [Ibn ʿAbbās, al-Ḥasan, Ibn Zayd]
2. It means that Allah restrains the hand of whom He wills from spending in His cause, and extends the hand of whom He wills to spend. [Abū Sulaymān al-Dimashqī and others]