'The first resurrection,' mentioned in Revelation 20:5, 6, does not mean a first resurrection, but the essence and primary part of resurrection, which is salvation and eternal life. There is only one resurrection to life. A second does not happen, and is not mentioned anywhere in the Bible.

(References: Apocalypse Explained 6; Apocalypse Revealed 851; Revelation 20:5-6)

Like most numbers in the Bible, "six" can have various meanings depending on context, but has a couple that are primary. When used in relation to time -- six days, six hours, six years, etc. -- six generally represents a state of labor, struggle and conflict, especially the conflict involved with spiritual growth. The six days of creation, for instance, represent the stages we go through in our lives, working toward the peaceful seventh day, in which our evil desires are removed from us and we can rest. In most other references, six represents all desires for good and all the true ideas that come from those desires for good -- or in the contrary sense, all evil and all the resulting false thinking.