Rom 2:7 "To those who by persistence in doing good seek glory, honor and immortality, he will give eternal life."
Now at first glance it may look as though these people, who fall into this category in verse 7, earn eternal life through their persistence in doing good.
But remember, whenever we come to the word of God we must view the bible as one book, which was given to many men over a period of many years. The Old and New Testament are God's word. The Old being a revelation of the Messiah to come; the New being the fulfillment of that promise.
God does not contradict Himself, and so we must compare scripture with scripture if we are to fully understand what God has to say on any subject.
So who are these people in verse 7 who apparently are able to work their way to heaven? This group of people are those who have a righteousness which comes from Christ, not themselves. In other words, this group of people are Christians who have believed on the Lord Jesus Christ for the forgiveness of their sins.
Their good works are not earning them eternal life, but are coming from thankful hearts to Christ who has given them eternal life. And, because they have the Spirit of Christ, they persevere in loving the Lord by doing good and seeking to glorify Him, as they seek the glory, the honor and the immortality He has promised for them.
We see this in what Jesus says in Luk 8:15 "But the seed on good soil stands for those with a noble and good heart, who hear the word, retain it, and by persevering produce a crop." A crop which is the outworking of our great God, whose hand is upon us to produce the kind of works which lift up the name of Christ -
http://www.cyberstreet.com/calvary/rm27-16.htm