Believers suffer through trials and tribulations in this life. Yet, Paul said that we could trust that God works all these for good because we love God and are called according to His purpose. Paul continued.
Romans 8:29 (KJV)
For whom he did foreknow, he also did predestinate to be conformed to the image of his Son, that he might be the firstborn among many brethren.
In the first phrase of this verse, "for whom he did foreknow", "he" refers to God. "Whom" refers back to verse 28, to those who love God and who are called. In other words "whom" refers to believers. Paul was revealing that God had known before the ages even began, who would be believers. In the second phrase, "he also did predestinate", "he" again refers to God. Besides foreknowing the believers, God predestined them.
These two rather simple phrases have led to unbelievable divisions in the body of Messiah. Primarily, the differences in understanding separate those known as Calvinists and those known as Arminians. However, this post is not intended as a proof on one side or the other. The debate between the two sides is multifaceted and beyond the scope of this post. At the same time, this discussion will touch upon the topic as the plain meaning of the text is dissected.
The word "predestine" means "to determine beforehand." Therefore, according to this verse God determines something in advance. This determination is based on God's foreknowledge. Large segments of Christianity believe that this means that God determines, in ages past, who is saved and who is not, removing any choice on the individual's part. But is this true?
God is omniscient. He knows everything. He also knows the future. But just because He knows that tomorrow John Doe will repent of his sins and trust in Yeshua, God did not cause him to make that particular choice.
Acts 2:23 (KJV)
Him, being delivered by the determinate counsel and foreknowledge of God, ye have taken, and by wicked hands have crucified and slain:
Similarly, this verse in Acts confirms that although God foreknew that Yeshua would be crucified and He allowed this to happen, it doesn't negate the responsibility of the wicked men who chose this course of action.
Still, the word "predestine" does mean "to determine beforehand." But in looking at the verse and at the context of what Paul was discussing, it is obvious that the topic is not salvation. This verse is part of Paul's teaching on why believers suffer. The second part of the "predestine" phrase, "to be conformed to the image of his son," also tells us what is being predestined. It is that God predestined believers to be conformed to the image of His Son, Yeshua. This is the goal of all the suffering that God uses for good.
Finally, the last phrase confirms that God's goal is to mold believers into a body of brethren, with Yeshua being the firstborn.
In summary: Through God's foreknowledge He predestined those whom He knew would be believers, to be conformed to the image of His son, Yeshua. This process of conformation often involves suffering. But the good that results is the molding of a body of Yeshua-like believers with Yeshua as firstborn.