“We are to invoke God alone in every need, and yet this does not exclude our requesting the help of others. For it is God who has conferred on them their ability to help and has appointed them “ministers” of his beneficence. Whatever benefit we receive from others we should regard as coming from God, who alone bestows every benefit through their “ministry.”
Then comes the interesting question (Q. 237): “But should we not be grateful to other people when they perform some service for us?”
Answer: “Of course we should, precisely because God honors them by channeling through their hands the good things that flow to us from the inexhaustible fountain of his generosity. In this way he puts us in their debt, and he wants us to acknowledge it. Anyone, therefore, who does not show gratitude to other people betrays ingratitude to God as well.”
B.A. Gerrish in Grace and Gratitude: The Eucharistic Theology of John Calvin (Eugene: Wipf & Stock, 2002) 44-45.