If he means that, according to Calvin, “ultimately” one is to ground there assurance on the objective promises of God then I have no problem with the statement. If, however, he meant that Calvin did not teach that the fruits of sanctification do not (or are not to) strengthen or help our assurance then I find that to be inaccurate.

Here is the quote by Calvin I am thinking of:

“A conscience so founded, erected, and established is established also in the consideration of works, so far, that is, as these are testimonies of God dwelling and ruling in us. Inasmuch, therefore, as this reliance upon works has no place unless you first cast the whole confidence of your mind upon God’s mercy, it ought not to seem contrary to that upon works, we mean only this: that the Christian mind may not be turned back to the merit of works as to a help toward salvation but should rely wholly on the free promise of righteousness. But we do not forbid him from undergirding and strengthening this faith by signs of the divine benevolence toward him. For if, when all the gifts God has bestowed upon us are called to mind, they are like rays of the divine countenance by which we are illumined to contemplate that supreme light of goodness; much more is this true of the grace of good works, which shows that the Spirit of adoption has been given to us” (3.14.18).

Note the words “founded” “erected” and “established”!

Ferguson, in a lecture he gave, persuasively argues concerning this quote:

“The interesting thing here to me is that already in Calvin you begin to see the deep-seatedness of his under-girding Trinitarian theology; that assurance is brought to the believer by the Father’s fatherly benevolence toward him through Jesus Christ who is worth a thousand testimonies, but also in the power of the Holy Spirit, not only with respect to the Holy Spirit’s witness to Christ, but with respect to his witness to the power of Christ to save in the fruit of his ministry; that is to say, the good works that the Christian believer does. And at the end of the day, we might say for Calvin that to give no place to good works in the “package deal” of assurance would be to cut off glorifying the Holy Spirit for the nature of his ministry in the believer.” Blessed Assurance and Bickering Theologians (lecture)

Whereas Lillback says that to “look at our good works [he uses the word holiness] for assurance would be to cheapen the work of Christ,” Sinclair says the exact opposite…namely, for the believer NOT to look at what the Holy Spirit does in the believer’s life in producing good works is to cheapen the ministry of the Spirit!!!!