The phrase "necessary precursor" refers to something that must happen or be done before another important event or result can occur. It is something that is required or essential in order for something else to happen successfully. Full definition
And we can improve the functioning of those capacities, either by actively supporting them with necessary precursors or by getting out of their way. (marksdailyapple.com)
But the other reason that developers are likely to adopt segwit is because it is a huge necessary precursor, along with the recently released CheckSequenceVerify to the Lightning Network. (coindesk.com)
Increased mainstream adoption of bitcoin is seen by many as a necessary precursor to a more stable currency. (hacked.com)