The hair represents the people of the nations of Israel. Most of the church is in the nations of Israel, primarily the United States and Canada. The church is represented in the "small number"—represented by the hair that he puts into his pocket—taken from the third group, which goes into captivity and is thrown to the "four winds," showing a measure of protection. However, he then takes a part from that group and throws it into the fire. Now hair is the most flammable part of the body, and surely, the fire must indicate death.
This can be connected with the fifth seal of Revelation 6: the martyrdom of the saints. One can also connect it with Revelation 3:10 and the "Philadelphians" who are kept from the hour of trial that comes upon the whole earth. The group that he took out of his pocket and threw into the fire (and are therefore consumed in the fires of tribulation) represents the Laodicean church. It surely seems to indicate that very few, if any, of them will survive through the Tribulation. Five separations are indicated here in Ezekiel 5, but only one very small amount is protected in the fold of his skirt.
John W. Ritenbaugh
A Place of Safety? (Part 1)
Other Forerunner Commentary entries containing Ezekiel 5:12: