How similar were Calvin and Bullinger in their understanding of the covenant? Very similar according to Lillback’s analysis in his book The Binding of God. Indeed at the end of Lillback’s doctoral dissertation he appends an English translation of Bullinger’s De Testamento.
It is not widely acknowledged that Calvin did not hesitate to speak of the covenant in terms of its “stipulations” and “conditions”. This is evident from his commentary on Genesis 17:1,2:
“In making the covenant, God stipulates for obedience, on the part of his servant… For this condition, he adopts children as his own, that he may, in return, obtain the place and the honour of a Father. And as he himself cannot lie, so he rightly demands mutual fidelity from his own children ….
We have said that the covenant of God with Abram had two parts. The first was a declaration of gratuitous love; to which was annexed the promise of a happy life. But the other was an exhortation to the sincere endeavour to cultivate uprightness, since God had given, in a single word only, a slight taste of his grace; and then immediately had descended to the design of his calling; namely that Abram should be upright”
(cf Institutes, II.x.8: ‘For the Lord always covenanted with his servants thus: ‘I will be your God, and you shall be my people.’ The prophets also commonly explained that life and salvation and the whole of blessedness are embodied in these words … He is our God on this condition: that he dwell among us, as he has testified through Moses.”
Calvin’s reference to be upright (integer) echoes Bullinger’s frequent emphasis in his writings.