The first seal can be found in Revelation 6:1-2 and reads as follows...
“Now I saw when the Lamb opened one of the seals; and I heard one of the four living creatures saying with a voice like thunder, ‘Come and see.’ And I looked, and behold, a white horse. He who sat on it had a bow; and a crown was given to him, and he went out conquering and to conquer.”
White is the symbol of purity. In the apostolic age the doctrine and life of the church was pure, and under the leadership of Christ and the living apostles, it went forth victoriously, carrying the gospel to the entire civilized world in that generation.
Without railroads, highways or space travel—without the printing press, TV or the internet—those first gospel messengers carried the good news to the whole civilized world in a very few years. As the apostle Paul said, “it was preached to every creature under heaven” (Colossians 1: 23).
One reason the church was pure during this time period was that it was busy working for others. The church that is busy working for the salvation of the lost has little church trouble. It’s when the members settle down to enjoy religion for themselves alone that the troublers of Israel get busy. And if the pastor does not watch out they will keep him so busy settling; their affairs and keeping them sweet that he will never get out after the lost sheep at all.