The strength that can unseal the hidden book is not force but the courage native to the higher self. Judah opens under its Hebrew root as praise, so the lion of that tribe is the fierce, praising power in a person that dares to face what is written within and read it. The root of David is the beloved center from which this courage grows.
The book stays shut to fear and weeping, and opens only to the part that has prevailed over its own dread. In plain words, the sealed truth about a person can only be read by the brave, grateful strength already alive inside them.
Lion of Juda: the fierce praising courage in a person, strong enough to face the hidden self and read it
Root of David: the beloved inner center out of which that courage grows
Book: the sealed record of a person's own nature, closed to fear and opened only by inner strength
7 seals: the 7 layered closures over self-knowledge, undone one by one as awareness rises