There is a debate in today’s daf (Ketubot 58b) about the principle of whether אדם מקדיש דבר שלא בא לעולם – ‘someone can consecrate something that has yet to come into existence’.
In terms of our daf, this principle is invoked with reference to yet-to-be earnt earnings, while a beraita discussing the laws of conversion is then quoted to demonstrate that commitments can be made even before a new situation has come into existence.
While considering this question the Yalkut Me’am Loez, in his commentary to Shmuel I 1:11, notes how Hannah, in her heartfelt prayer seeking to have a child (which is read as the Haftarah on the first day of Rosh Hashanah), vowed: “Lord of Hosts, if You look down with sympathy on the misery of Your handmaid and recognize me; if You do not forget Your handmaid and grant Your handmaid a son, I will then give him to the Lord all the days of his life”. Based on these words it certainly seems that someone can consecrate something that has yet to come into existence.
However, in answering this question he then quotes Rashi’s commentary on this verse who explains that when Hannah said ‘I will then give him’, it seems that she meant, שיהא ראוי לתתו לה’ – ‘that he should be worthy to be given to divine service’. Still, as the Rambam explains in his Hilchot Arachin V’Charamim 6:31, ‘it appears to me that even though a person cannot consecrate an entity that has not come into being, if they say: “I pledge to consecrate it,” they are obligated to consecrate it when it will come into being to [fulfill] their vow’. What this suggests is that while a person cannot consecrate an item (חפצא) before it has come into existence, if a person (גברא) makes a pledge about something that has yet to come into existence they must nevertheless fulfil it because the pledge has been made by a person who already exists.
Having said all this we can now reflect on why this Haftarah is read on Rosh Hashanah, and while there are many reasons given for this choice, what we learn from here is that these verses teach us about commitment and being true to our word – even about things that are beyond our control, or have yet to come into existence.