The phrase "prime importance" means something is extremely significant or crucial. It indicates that it is the most important or primary focus in a given situation. Full definition
... The provincial superior courts have always occupied a position of prime importance in the constitutional pattern of this country. (politics.stackexchange.com)
If you've read my site before, you know how adamant I am about blood sugar stabilization being of prime importance in any health issue. (robdaquila.com)
Two things which occur to me of prime importance for Labour — 1. (compassonline.org.uk)