1. I am going with the assumption that community transmission might have started at some location; but with that assumption this 21-day lockdown becomes an imperative and excellent step.
2. Will people obey the lockdown? (This is not a curfew, as essential services would be open.) Many people, sadly, would not. That is where the sometimes-criticized high-handed approach of police and other agencies would be useful.
3. I am optimistic about this period. At the end of it, if nothing else, we would have more data points to make thoughtful decisions about how to proceed and what other measures need to be taken.
4. Testing is being ramped up, and I hope it is an exponential ramp-up. Local test kits are also approved and beginning production today.
As a nation with 4X the population of the USA, and 1/3rd the area, the population density in India and particularly in the urban areas is off the charts. Hence, the approach suggested in some other countries, like carrying on with walks, exercises and other outdoor activities while practicing 'social distancing', gets much more difficult.
It is nearly impossible to be outdoors in urban areas and not have people nearby. As such, measures have to be very strict. I imagine the situation was similar in Wuhan in China, and they had to impose a complete lockdown as well.