Let's consider an analogy
Suppose there are two movie makers at Hollywoood, James Calvin and Matt Chandler. James Calvin is a very famous movie producer who mentors his actors after pre-selecting them and compelling them to be be mentored by him.
Matt Chandler invites whoever wants to be mentored by him to join his team voluntarily. However, one thing they both have in common is that prior to the actors being chosen for a particular movie, both movie producers had predetermined to conform their actors into well-conditioned and trained characters.
Calvinists get it wrong
Calvinists insist that Ephesians 1 teaches that God is like James Calvin but all the text actually states is what the movie producer has predetermined for his team to become, it says nothing about his predetermining who would and would not be chosen (i.e. “in Him”).
What should we be asking?
The question should be how does one come to be in him? Has God chosen individuals to be placed in Him? Or has God chosen individuals who choose to be in Him? In other words, has God predetermined the individuals to be in the group? Or has God chosen a group of individuals for a predetermined end?
Some fixate their eyes so much on the first 12 verses that they literally ignore the last two verses where Paul gives an answer to this vital question; “How does one come to be in Him?”
Ephesians 1:13-14
And you also were included in Christ when you heard the message of truth, the gospel of your salvation. When you believed, you were marked in him with a seal, the promised Holy Spirit, who is a deposit guaranteeing our inheritance until the redemption of those who are God’s possession—to the praise of his glory. —Ephesians 1:13-14
Two questions to consider
First question: When were you included in Christ? Was it before the foundation of the world? Or was it when you heard the message of truth, the gospel of your salvation?
Second question: When were you marked in Him? Was it before you were born or had done anything good or evil? Or was it when you believed? What does the text say? Decide for yourselves!
For more information on this topic, visit Soteriology 101