Speaking of the non-Israelite mariners (Jon 1:5-7), we read the following in the book of Jonah:
Then they cried out to the Lord, "Please, O Lord, we pray, do not let us perish on account of this man's life. Do not make us guilty of innocent blood, for you, O Lord, have done as it pleased you." So they picked Jonah up and threw him into the sea; and the sea ceased from its raging. Then the men feared the Lord even more, and they offered a sacrifice to the Lord and made vows. (Jon 1:14-17)
This is rather instructive as it shows that, on the basis of these non-Israelites' petitionary prayers, vows, and even their sacrifices, God was propitiated to the point that He stopped the storm against their ship and accepted all these works, including sacrifice which was the highest form of cultic worship in the Old Testament. Indeed, the Hebrew in v. 16 does not allow for anything but cultic sacrifices, not merely spiritual, using the word which literally means "to slaughter" (זבח) and the LXX uses the verb which means "to sacrifice" (θυω). However, as people were not members of the covenant, in the Calvinist view, God would not have accepted their works at all, instead, would have rejected them as acts of idolatry from pagans and/or those simply feigning belief in the true God yet being an idolater at heart. This is seen in the following comment from a Jewish scholar:
a sacrifice … vows Their sacrifice is to be understood not as a collective but as a genuine singular: to express their spontaneous thanks they sacrifice to the Lord, right there on the deck of the ship, one of the animals they had taken aboard for food. Their vows, however, are in the plural: to express their continuing gratitude and perhaps also to make it widely known, each of them vows to bring a sacrifice when he reaches his destination. Kaufmann (p. 282) notes that this does not mean that they abandoned their pagan creeds and adopted the faith of Israel; it is simply a magnification of the glory of the Lord among the nations, such as we find in the stories of Elijah (1 Kings 17:24) and Elisha (2 Kings 5:15–18; 6:12, 23; 8:7–15). (Simon, Uriel. (1999). Jonah (p. 15). Philadelphia: Jewish Publication Society.)
Such makes no sense in light of Reformed theology, and is yet another passage from the Bible which shows that Reformed Protestantism is a far cry from what can be, using sound exegesis, "Biblical Christianity."