Here's an excerpt that explains it:

[link to www.endtime.com]

The teaching of the four blood moons has recently captivated the attention of the religious world. This teaching states that, when four consecutive blood moons fall on Jewish feast days, a major event affecting the Jewish people will occur in close proximity to that time.



This phenomenon of four consecutive blood moons coinciding with Jewish feast days has only occurred ten times since 1 AD and only three times since 1492 AD. The three times since 1492 are as follows:

Tetrad of 1493-1494
Tetrad of 1949-1950
Tetrad of 1967-1968

Major events affecting the Jewish people have occurred in close proximity to all three of these tetrads.


The Spanish Inquisition Took Place in 1492 Just Before the Tetrad of 1493-1494

In 1492, King Ferdinand and Queen Isabella of Spain gave the Jewish population a mere four months to convert to Catholicism or leave the country. It is estimated that between 165,000 and 400,000 Jews fled the country at this time. As many as 50,000 decided to stay, converting to Roman Catholicism.

....

Four Blood Moons Just Ahead

Four blood moons on Jewish feast days are getting ready to appear for the fourth time in the last 500 years. According to NASA, they will occur on:

April 15, 2014—Passover
October 8, 2014—Feast of Tabernacles
April 4, 2015—Passover
September 28, 2015—Feast of Tabernacles

Some prophecy teachers are declaring boldly that this tetrad just ahead signals that something is getting ready to happen, which will change the world forever.