Same idea as the "cash injection" done a couple of season's ago, additional funding for player acquisition in return for some equity.
Spurs is not United/Pool/Chelsea where there is a ton of infrastructure spend required (we can absolutely fund the hotel/other real estate investments without external help)
Levy has been asking for this for years (rumours are Lewis said no twice before the 150m), we have increased our spending on squad (since Chelsea takeover we are 3rd in both gross & net spend on players) but we have a gap to make up.
This club, with it's current facilities, current turnover, in Europe, given another 300M (above normal) to spend on 2-4 finished article players? could establish us as a top 4 (Pool made that step with VVD, Allison and the addition of Jota) all the time vs. challenging for it.
Re the ethics of the money, everyone will have to make that call themselves, any non debt related cash injection is likely to have some concerns in origin.