Some quotes from Calvin on covenant and election issues.
"So it was in France, Italy, Germany, Spain and England after the Lord established his covenant there. When those countries were oppressed by the tyranny of the Antichrist, the Lord used two means to keep his covenant inviolable. First, he maintained baptism there, a witness to this covenant; consecrated by his own mouth, it retains its force despite the impiety of men. Secondly, by his own providence he caused other vestiges to remain, that the church might not utterly die.”
[Calvin, Institutes, IV.II.11 (2:1051-1052)]
“But there is also another reason in our case, when God receives us into his favour; for we were covenant-breakers under the Papacy; there was not one of us who had not departed from the pledge of his baptism."
[Calvin, Commentaries, (13:115)]
“For when they claimed for themselves the name “church,” they wanted belief in the gospel to depend upon their decision. Today, in like manner, the papists with this false pretext would willingly substitute themselves for God. Paul, although he admits that, by virtue of the covenant, the offspring of Abraham are holy, still contends that many among them are outside of it. And that is not only because they degenerate from legitimate children to bastards but also because God’s special election towers and rules over all, alone ratifying his adoption.”
[Calvin, Institutes, III.XXI.7 (2:931)]
So, for Calvin,
a. Baptism does something - it witnesses to the covenant and brings with it the obligation to abide by the terms of the covenant.
b. By virtue of the covenant someone can be 'holy' in a way but really be an outsider from the perspective of special election.
c. There is such a thing as covenant-breaking in the new covenant.
d. God's special electing grace is sovereign over adoption and apostasy.