Dear brothers, Allah the Almighty said:

(And as to those who believed but did not emigrate (to you O Muhammad PBUH), you owe no duty of protection to them until they emigrate…)

Allah wanted to encourage them to migrate, when you migrate you have the same right and duties of the believers.

The wide and narrow meaning of Hijra:

What is the meaning of the verb (haajara) in Arabic? There is also the verb (hajara). When you live in a house that you don’t like, you leave it (here we use hajara) but when you are annoyed and you can no more bear it we say (haajara). 
Had the companion been allowed to spread their religion in Mecca and worship their Lord, there wouldn’t have been a reason to migrate. However, they were annoyed, tortured, besieged, and some of them were killed. This forced them to migrate. Thus, we need to distinguish between the verb (hajara) which means leaving a place, and (haajara) which means that someone was annoyed and forced to leave a place.
Hijra in its wide meaning is to move from the place of disbelief to a place of belief, if we make it wider, it is to move from a job that doesn’t please Allah as it implies clear sin to another job that pleases Allah, or to leave a friend that doesn’t please Allah to another one that pleases Allah.