As JT says, context is key here.
I can imagine that sentence really meaning "gross weight [as defined above] is minimum required for flight" - meaning that the document defines a weight, and is saying you mustn't go below it - which could speak to VMC or other considerations.
I can also imagine it really meaning "gross weight is [to be the]minimum required for flight" i.e. keep the aircraft as light as you can, with no lower limit.
The nature of the ferry might give a clue; if it was a ferry with significant airframe or systems damage (to get to a repair base) that might yield clues.
In our case, we've had some ferry flight permits where the aircraft had to be kept as light as possible, to minimize loads for example, and some where a minimum flight weight had to be achieved to respect VMC in light of system defects.