I like Fr. Lawrence's explanation so I will show it:
This understanding of
proginosko also informs St. Paul’s meaning in
Romans 8:29, where after saying that God causes everything to work together to help us in our salvation (v. 28) he writes, that those “whom He foreknew, He also predestined to become conformed to the image of His Son, so that He might be the first-born among many brethren”. The word translated “predestined” is the Greek
proorizo/ προοριζω, literally to pre-appoint,
orizo meaning “to appoint, to order, to designate”. The word
orizo is used of a prophet ordering a meal (in Didache 11:9), and of God appointing Jesus Christ to be the Saviour (in Acts 17:31), and of Him designating Jesus as the Son of God by raising Him from the dead (in
Romans 1:4). The word
proorizo therefore means that God pre-appointed those whom He foreknew would believe in Jesus to be conformed to Christ’s image. The emphasis in not on individual’s choice for or against Christ, but on corporate destiny; it does not answer the question, “Who gets saved and how?”, but rather, “What is God planning to do for those whom He foreknew would believe?” The answer: their destiny is to be conformed to the image of Christ, so that all that Christ is by nature He shares with them by grace. Thus Christ is but the first-born of many brethren; all of God’s people are pre-appointed to be like Jesus.