What was the basis on which alcohol (khamr) was initially permitted?

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

1. It was permitted by the verse, "And from the fruits of the palm trees and grapevines you take an intoxicant (sakar)." (16:67) [Ibn Jubayr]
2. It was permitted by the previous lawcode (of past prophets), and the Muslims were allowed to continue with it until it was eventually prohibited.