What's wrong with a salvation that's by faith in Christ plus doing good works? Eventually and ultimately, you will trust in the latter more than the former, making you, essentially, trust in your good works alone for salvation. Just as you can't serve two masters at the same time so you can't trust in two Saviors equally at the same time. The focus of one's trust in this scheme will gravitate toward the good works part. Since Christ's work and part are already done so the heart will now focus on doing the good works part which will have to be an endeavor that will go on for life. At the bottom of things, it all boils down to trusting in good works for salvation. It necessarily results in the denial of Christ alone as Savior.
