Garabandal is Our Lady's response to 1) the failure of John XXIII to reveal the Third Secret and 2) to the putting aside of the orthodox preparatory schemas for Vatican II around October 1961. Garabandal is a continuation of the Fatima message.
The first message of Our Lady to the children at Garabandal took place on October 18, 1961. Right around this time the scrapping of the orthodox preparatory schemas took place according to Fr. Henri de Lubac (
link).
Around the same time in October 1961, John XXIII called an Audience of Italian Journalists, where all the big newspapers in Italy sent a representative (
link). This was the shift from Vatican II as a "Church Council" to a modern public relations campaign.
Our Lady, in response to these events, initiated her own kind of "public relations campaign." Go back and read the Garabandal messages and events in this context and I think you will understand its importance.
The Warning and Miracle are definitely Scriptural. But beyond Scripture, each of Our Lady's messages has included a "Warning" and a "Miracle." So to reject Garabandal on those grounds seems ridiculous.