Satan told a lie that had enough truth to be convincing.  That's what he always does.   God cannot lie.  Satan always lies.  Satan meant this for evil, and that evil enemy continues to tempt every man and woman to struggle to try to become gods.  That is at the core of many of the useless cults such as New Age Religion, Alien false religions, and Secular Humanism.

Yet, God said, "I have said, Ye are gods; and all of you are children of the most High." Psalm 82:6  "Jesus answered them, Is it not written in your law, I said, Ye are gods?"  John 10:34 

God obviously means something by this--and that something is quite different from what that old liar, Satan said.   If we state Romans 8:28-29 in plain English, it says that God is working everything together to bring about His good purpose for those who love Him and who are called according to His good purpose.  His good purpose is that we "be conformed to the image of his Son, that he might be the firstborn among many brethren."  We may not exactly know the details of this purpose that God has in mind for us, but we know that it's going to be very, very good.

You can find out more about what God meant here: http://seekfind.net/Find_True_Love.html

http://seekfind.net/Gods_Purpose_Is_To_Have_You_Grow_Up_To_Maturity.html

http://seekfind.net/GodsPurposeForOurLivesIsThatWeBecomeLikeJesus.html