Although we are not permitted to hold weddings during these days, Halacha allows a person to become engaged—even on Tisha B'Av itself. The Gemara explains the reason: שמא יקדיםנו אחר —perhaps someone else will marry her first. But the Gemara then raises a question: If a person's zivug is already determined even before conception, how could anyone else take what was destined for someone? The answer: if the other person prays hard enough, he may merit it. From here we learn the incredible power of tefillah: It can change what has already been decreed. The Gemara in Masechet Berachot states that one can pray for the gender of a fetus only until the 40th day after conception. After that point, it is considered a tefillat shav —a vain prayer. However, the Yerushalmi in Berachot writes that even if a woman is already in labor, tefillah can still change the gender of the child. Even though we follow the Bavli and do not pray for a gender change after 40 days, the Sefer Berumo Shel Olam explains that the disagreement is only about whether one may pray for a miracle—but all agree that prayer itself retains the power to change reality, even up to the moment of birth. We find an extraordinary example in the case of Chizkiyahu HaMelech. The Navi Yeshayahu came to him and told him that Hashem had decreed death upon him—because he did not fulfill the mitzvah of peri'ah v'revia , having children. Chizkiyahu, although righteous, had seen through prophecy that he would father a wicked son and therefore refrained from marrying. Despite his reasoning, he was held accountable. Chizkiyahu then asked Yeshayahu if he could marry the prophet's daughter, in the hope that their combined merits would produce righteous children. But Yeshayahu answered: It's too late—the decree has already been sealed. Chizkiyahu turned his face to the wall and poured out his heart in prayer. And indeed, Yeshayahu was immediately told to return and inform the king that Hashem had added fifteen more years to his life. Many ask: Why didn't Yeshayahu know through prophecy that tefillah would change the decree? The Kad HaKemach answers: Tefillah is higher than prophecy. It stems from a level in Shamayim beyond where nevu'ah can reach. Even a prophet cannot see what changes tefillah might bring. Another powerful example is Leah Imeinu. It was decreed before she was born that she would marry Esav. But through heartfelt tefillah, she changed her destiny—and instead married Yaakov Avinu, the Gadol HaDor . The Gemara in Masechet Niddah asks: What can a person do to become wise? It answers: He should study Torah and pray to the One who possesses all wisdom. The Maharsha explains that the question refers to someone whose natural intellect was limited due to a Heavenly decree. Can such a person become wise? The Gemara answers: Yes—if he learns Torah and prays sincerely, even he can attain wisdom. Through Torah and tefillah, one can rise above natural limitations. There is nothing that tefillah cannot accomplish. Therefore, it is our responsibility to use this powerful gift with all our strength. Even if we feel that we've prayed many times and nothing has changed—we must continue. The Gemara tells us, חזק ויאמץ לבך וקוה אל ה —strengthen yourself, and do it again. There is no limit to what effort in tefillah can achieve. We must keep renewing our strength, returning to prayer again and again, pouring out our hearts with sincerity and Emunah.