Question

Why was the liberator important to the antislavery movement apex?

Answer 1

it was a highly influential abolitionist newspaper

Answer 2

Spread ideas of the movement--The Liberator was the newspaper for the abolitionist movement and spread the ideas of the movement to the people of the US in particular the North. 

The Liberator published by William Lloyd Garrison, published the ideas of the abolitionist movement. The paper published stories of former slaves and ways people could help with the movement.