This verse is about the body of Christ. There will be a class of individuals who conform to preordained standards. The Heavenly Father planned this class even before the foundation of the world. God purposed to grant the Christ (Jesus and His body members) a place of glory, honor, and immortality. (Romans 2:7; I Corinthians 15:53)
To give an illustration, let's suppose a person decided he wanted to have a sports team. Even before the individual members were selected, it was predetermined that the team would exist. Let us also suppose that all of the criteria for the team were predetermined: the number of team members, the positions, the abilities, a team captain, etc. All of these factors were established years before the team came into existence. Sometime later a general announcement is made for tryouts for the team. This tryout is not mandatory; but those who do tryout, meet the qualifications, and actually make the team could be thought of as being the elect of this predestinated team.
These same principles apply to God's selection of the Church. Ephesians 1:4,5 explain that before the foundation of the world, God purposed to have, through Christ, a select class brought to sonship. The qualification was they must conform to the character image of His Son. (Romans 8:29) Following the team illustration, God predestined that there shall be a class with Christ as the head and the church as His body. (Ephesian 1:22,23) The individual members that were not predestinated, but the collective as a whole was. Paul in Romans 8 tells us how God goes about finding individuals that fit into this elect class. The process is described in verse 30 but is listed in reverse order (predestinated, called, justified, and glorified).
The process starts with those he "glorified," (Greek word "doxazo," Strongs #G1392). This word is usually translated as "glorified," but the word also means "honor." (For an example, see I Corinthians 12:26.) From the context of Romans 8:30, the correct translation should be "honored."
So how was this class honored? They were honored with the knowledge of the Gospel, for the sound went into all the earth. (Romans 10:18, I Peter 1:12). Those who He honors with the Gospel and knowledge of Christ, He justifies through Christ. Those who are justified through Christ are called to be of the predestinated class. Thus, although it was preordained that individuals should make up this predestinated class, it is of their own "free will" that they enter into this relationship with God. In this relationship, they strive to be copies of His son Jesus Christ who was the first born of this class. (Colossians 1:18, Romans 8:29) This is the class that God purposed and preordained before the foundation of the world.