See in Reader
940 B
those whom he foreknew
"those whom he knew before he even created them"
he also predestined
"he also made it their destiny" or "he also planned in advance"
to be conformed to the image of his Son
God planned from before the beginning of creation to grow those who believe in Jesus, the Son of God, into persons who are like Jesus. You can translate this in an active form. Alternate translation: "that he would change them to be like his Son" (See: rc://en/ta/man/translate/figs-activepassive)
Son
This is an important title for Jesus, the Son of God. (See: rc://en/ta/man/translate/guidelines-sonofgodprinciples)
that he might be the firstborn
"so that his Son would be the firstborn"
among many brothers
Here "brothers" refers to all believers, both male and female. Alternate translation: "among many brothers and sisters who belong to the family of God" (See: rc://en/ta/man/translate/figs-explicit)