Overturning God's Eternal Purposes

I have recently begun studying through Ephesians, and have been going over 1.1-6. The heavy emphasis on God's eternal and free election and predestination of us as the basis of our salvation, sanctification, and adoption is immediately apparent. The conclusion of Paul is that God's blessing of us through election is ultimately 'to the praise of his glorious grace which he bestowed on us in the beloved.' Therefore, Calvin notes (Commentary on Ephesians, in loc.), any countering of the doctrine of God's election is extremely serious:

Every man, therefore, who hides this glory [based on election], is endeavouring to overturn the everlasting purpose of God. Such is the doctrine of the Sophists, which turns everything upside down, lest the whole glory of our salvation should be ascribed undividedly to God alone.