From Sinclair Ferguson’s lecture “Blessed Assurance & Bickering Theologians” (iTunes):
“Calvin’s great emphasis in The Institutes is that the Christian life is adoption into the family of God and that he is such a father as you would hope to be yourself as a father, who desires to leave his children no doubt whatsoever whether they really are his or not.
Part of the drive in Calvin to focus on Christ is a drive against the demonic doctrine of God that he saw in the Roman Catholic Church because it presented a father who needed a gentler son and a gentler son who needed an even gentler mother in order that the son’s arm might be twisted, that the father’s arm might be twisted, until at last—contrary to their better judgments—to give grace and salvation to lost sinners.
So you can understand the thrill and the joy of the reformation, to discover that the son is not hidden behind his mother, that the father is not hidden behind the son, but the son fully discloses the heavenly father. And as heavenly father his desire is not to leave his children in doubt, whipping them constantly into a spirit of bondage but to give to them the spirit of sonship by whom they cry ‘Abba! Father!’ [Galatians 4:6]. This explains the vigor and the joy that we find in the expressions of assurance both in Luther, but particularly in Calvin, whose theology is dominated by the wonderful release of having certitude. A huge motif in Calvin’s theology is this: The gospel gives us certitude.”