According to the Torah, the Temple Mount is the holiest place on earth. Adjacent to it lies the Western Wall, last remnant of the 1st and 2nd Jewish Temples, both destroyed over 2,000 years ago. The Kabbalah states that the presence of G-d will always dwell at the Wall. For this reason, people of all faiths have been pilgrimaging to the Western Wall for centuries, to cry out to G-d to heal them from all their ailments.
By secular and Jewish law a person can appoint an agent to act on his/her behalf. By having an agent to pray for you, it is as if you were actually standing at the Western Wall (Kotel) in person.
Am I taking a short-cut?
A righteous person (Tzaddik) was once asked why one should come to them for a blessing. After all, if G-d bestows suffering on individuals in order for them to turn to Him and come closer to G-d (do teshuva), then why should one ask a Tzaddik to help take it away? Isn't that against the point of the suffering - personal growth?
The Tzaddik answered that just as G-d sometimes sends messengers to deliver the suffering, He also sends messengers to lessen the suffering. There are no coincidences; the specific pain was sent for a reason, and it is please G-d, taken away at the right time. The messenger is just the vehicle.
It is important to note that the 40 day Segula is not meant to be a rabbit's foot, or replacement for your own personal growth, but an extra resource that G-d gave you in order to arouse His mercy.
Also, according to Judaism, 3 things annul an evil decree: prayer, charity and repentance. Through the 40 days of prayer, the charity given at the Wall and your personal 40-day work, you will G-d-willing fulfill another method of arousing G-d's mercy and be much closer to being a fitting emissary to receive the blessing you want.
Since we cannot play G-d, we offer no guarantees. However, with Torah-learning, heart-felt prayers and good deeds we do our best!