For Edwards, the idea of "The bow of God's wrath is bent, and the arrow made ready on the string" helps to convey the urgency of the moment. This urgency is one in which Edwards claims that God is angry right now, at this moment and is ready to take action against those who are "sinners." Edwards has his audience in mind when he speaks of the bow and arrow of God's anger. He recognizes that some individuals might feel that the anger of the divine is something that can offset with time or something that is in the distant future. This would enable the individual to engage in more sin and transgression.
Yet, this condition is not something that Edwards sees. He wishes to convey that God is angry right now with the amount of transgression being displayed. This anger has a form of the immediate attached to it in how the bow is ready and the arrow is prepared. For Edwards, this condition is one of urgency, intended for individuals to change their ways right now. The sense of immediacy in the need to reform is a part of why Edwards embrace this image to convey God's anger and the sense of wrath associated with it.
Edwards' sermon is an attempt to awaken people's faith on God again. During Edward's time, the modern science and logical reason gave rise to the Enlightenment movement, which was about beiving in facts that could be proved by science and understood logically by reason. The Enlightement movement, therefore, caused people to begin doubting their religious faiths. In an aim to bring people back to faith, Edwards preached about the mercy and the wrath of God.
Edwards probably thought of this line, "The bow of God's wrath is bent, and the arrow made ready on the string" from reading King Lear by Shakespear. In King Lear Act 1, Scene 1, Ln 146, King Lear threatens Kent to kill him if he continues to contradict him: "The bow is bent and drawn. Make from the shaft." Here Lear warns Kent that "the bow is bent" or that he has no more patience or mercy for him and that he is ready to snap; that Kent needs to stop confronting Lear or "move from the shaft" because if Kent doesn't obey, Lear will let go of the arrow any time.
Similarly, Edwards warns people who have gone astray from practicing their Christian religion that "the bow of God's wrath is bent" or that God's power is ready to snap. In the context of Edwars, he probably uses this language to show people that the only thing that is holding God to not let go of the arrow is God's patience and mercy. However, Edwars' point is that God's bow or power is loaded with his arrow or anger and is stringed or ready to shoot and kill or destroy. Edwards uses this image as an attempt to bring people to fear of God so that they can be converted and therefore saved.
the link with the underlined word, sermon, does not have anything to do with the answer. I don't how that happened.