The question is asked of the Beracha that we say in the Amidah. We say "Veishe Yisrael Utefilatam, Meharah Bia’hava Tekabel Beratzon." Which literally means, ‘Ishe Yisrael ‘, the fire of Israel, which was referring to the Karbanot of Yisrael, and their prayers, that they be accepted speedily. So the question was asked of the Ben Ish Chai in his Sefer Torah Lishma; how can we pray to G-d that the Karbanot be accepted, while today without a Bet Hamikdash, we have no Karbanot? What is the meaning of the "Ishe Yisrael"?

So the Tur in seman 120, explained it, that even thought today without the Mizbeach and without the Bet Hamkidash, we do not have official Korbanot, but the prayers that we make, whether it’s the Amidah or the different readings of the Ketoret, or the Parshat Tamid, etc, that we do on a daily basis, that they have a status as if we brought the Korbanot. So therefore we are saying the ‘Ishe Ysirael’, in the Korbanot that we brought to you in the form of Tefilah, that it is considered as if we brought a Korban, so that it should be accepted with our regular Tefilot, that we are praying.

Another explanation is brought down in the Midrash. That Micha’el, who’s the Sar Hagadol, the angel in heaven who is the one that brings the Neshamot of the Tzadikim on the Mizbeach in front of G-d which atones for the Jewish people. So we are praying to G-d, ‘Veishe Yisrael’, that the Korbanot that are brought by Micha’el in heaven should atone for the sins of the nation on Israel, and be a Kaparah.

Lastly, the Ben Ish Chai gives a 3rd explanation, that says when a person fasts, it is as if he is doing a Korban in the sense that he is diminishing from his blood and his flesh, and therefore it is as if that sacrifice of not eating, therefore diminishing a person’s physical stature, that is as if one brought a Korban to Boreh Olam. As the Gemara says, that Rabbi Elazar, after a fast day, he used to pray at the end of the Amidah and say, [listen to the audio clip for exact quote,] ‘that it is evident and clear in front of you that I brought in front of you today my flesh and my blood, and that the smell that emanates from my mouth on this fast day should be considered like the aroma of the Korban Olah, and accept me.’ So therefore, when a person is fasting, that’s also considered a type of Korban. Therefore he says that’s also the Kavanah (meaning), ‘Veishe Yisrael’, that the Korbanot of Israel on the fast days, is that they sacrificed their flesh and blood to G-d, that such should also be accepted in front of Boreh Olam as a Korban.