Pharaoh’s heart is stubborn
The Hebrew word for "stubborn" is "kaved," which can also mean "heavy" or "hardened." This description of Pharaoh's heart is significant, as it reflects his resistance to God's command. In the ancient Near Eastern context, the heart was seen as the center of will and decision-making. Pharaoh's stubbornness is not just a personal trait but a spiritual condition that opposes God's will. This phrase foreshadows the ongoing struggle between God's purposes and human obstinacy, a theme that resonates throughout the biblical narrative.

he refuses to let the people go
This phrase captures the core conflict of the Exodus story: the liberation of the Israelites from Egyptian bondage. The Hebrew verb "refuses" (ma'en) indicates a deliberate and conscious decision by Pharaoh to oppose God's command. This refusal sets the stage for the dramatic series of plagues that follow, each designed to demonstrate God's power and compel Pharaoh to release the Israelites. The historical context of Egyptian slavery and the Israelites' cry for deliverance highlight the significance of this moment as a pivotal point in God's redemptive plan for His people.

(14-21) The water turned to blood.--Moses had already been empowered to turn water into blood on a small scale (Exodus 4:9), and had exhibited his power before his own people (Exodus 4:30). But the present miracle is different. (1) It is to be done on the largest possible scale; (2) in the sight of all the Egyptians; and (3) not as a sign, but as a "judgment." All the Nile water--whether in the main river, or its branches, or the canals derived from it, or the pools formed by its inundation or by percolation through its banks, or in artificial reservoirs, including the tanks of wood or stone attached to houses (Exodus 7:19)--is to be "turned to blood:" i.e., not merely turned of a red colour, either by admixture of earthy matter or of Infusoriae, but made to have all the qualities and appearance of blood, so as to become offensive, horrible, loathsome (Exodus 7:18). The judgment strikes the Egyptians two several blows. (1) It involves an insult to their religion, and brings it into discredit, since the Nile-god, Hapi, was a main object of worship, closely connected with Osiris, and even with Amnion, celebrated in hymns with the most extravagant titles of honour (Records of the Past, vol. iv. pp. 108-110), and a frequent object of public adoration in festivals. (2) It is a great physical affliction. They are accustomed to use the Nile water for drinking, for ablutions, for the washing of their clothes, and for culinary purposes; they have great difficulty in procuring any other; they delight in the Nile water, regard it as the best in the world, are in the habit of drinking deep draughts of it continually. This is all put a stop to. They suffer from thirst, from enforced uncleanliness, from the horror of blood all about them, even in their cisterns. Again, their fish are killed. Fish was one of their principal foods, perhaps the main food of the common people; and the river was the chief source whence the fish supply was obtained, for even the Lake Moeris was an off-shoot from the river (Herod. ii. 149). Their fish supply is stopped. The punishment is retaliatory: for as they had made the Nile the means of destroying Hebrew infants (Exodus 1:22), so that Hebrew parents had loathed to drink of it, as though stained with the blood of their children, so is it now made by means of blood undrinkable for themselves. The plague lasts seven days (Exodus 7:25), a longer time than any other; and if not so destructive as the later ones, was perhaps of all the most nauseous and disgusting. . . .