Jesus opened the first 4 seals of the scroll revealing the things that will happen in the last days. The opening of the 4 seal corelates to the 4 horsemen of Zech 6:1-7 which speaks of God’s judgement on the nations. 4 represents the 4 corners of the earth. Compare also with Matt 24:4-8 where Jesus taught on the signs of the end of the age.