I believe that the white horse in Rev 6 is our promised comforter, the holy spirit. He is white, symbolizing purity, he has a crown, which is our promised inheritance from God. (let noone take your crown!)  and the bow he carries is not a weapon, but a bow we can see when the sun meets the rain; it is a reminder of Gods promise to us, to never again destroy the earth with water.
Many argue that the white horse is the antichrist, but I do not believe that. White means exactly what it is: pure, Godlike. God is not the author of confusion.
Jesus told us it was EXPEDIENT that he go away, so that the COMFORTER would come! The holy spirit is conquering souls through those who BELIEVE. Remember that we are not fighting against flesh and blood, but against spiritual wickedness, in high places. Satan is the prince of this world, and we are to overcome him through>> the holy spirit. Isn't that wonderful!!
Jesus said NOT to seal the words of Revelation because the>> TIME  WAS  AT  HAND!
and the first seal (I believe) was opened at his death.