"Their characters must be conformed to His character and their wills to His will. AA 549.1"
"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."
Both passages discuss the idea of believers being conformed to the image or character of Christ. Romans 8:29 speaks of predestination to conformity, while the EGW passage speaks of character and will being conformed.
"Let this mind be in you, which was also in Christ Jesus:"
Both passages emphasize the importance of having the same mind or character as Christ. Philippians 2:5 directly calls for this, while the EGW passage speaks of conforming characters to Christ's character.