A "creeper" is a plant that grows round posts, fences, trees, over walls, etc., like ivy. Similarly, the Law entwines itself through every aspect of our lives.
The second line implies that the individual and the social group to which that individual belongs are interdependent. Thus the strength of an individual lies in his social group (e.g. his family, or his society in general); while the strength of a social group lies in its members.
Does that help at all?
All the best,