The Gemara in Masechet Berachot (55) establishes that refusing to go to the Torah to recite the Beracha when called for an Aliya could potentially shorten a person's life, Heaven forbid. Moshe Rabbenu declares in the Book of Debarim (30:20), "For it [the Torah] is your life and the length of your days"; meaning, through Torah a person earns long life. The Gemara thus infers that one who refuses to go to the Torah for an Aliya forfeits the benefits of the Torah, and thus runs the risk of having his life shortened, God forbid.
The Gaon of Vilna (Rabbi Eliyahu of Vilna, 1720-1797) commented that this concept underlies an interesting Halacha codified in the Shulhan Aruch (Orah Haim 135:6; listen to audio recording for precise citation). The Shulhan Aruch there addresses the case of a Kohen who arrived in the synagogue as the congregation began the Torah reading. As there was no Kohen in the synagogue prior to this Kohen's arrival, the congregation called a Yisrael to the Torah. The Shulhan Aruch rules that if the Kohen arrived only after the Yisrael recited the words "Baruch Ata Ado-nai" in the Beracha, then the Yisrael should complete the Aliya. Since he had already begun the Beracha, he should not be interrupted and replaced by the Kohen. If, however, the Kohen arrived before the Yisrael began reciting the Beracha, while the Yisrael recited "Barechu," then the Kohen is called to the Torah instead of the Yisrael. Interestingly, the Shulhan Aruch adds that in this case, the Yisrael should remain next to the Torah during the Kohen's Aliya and during the Levi's Aliya, and then he – that same Yisrael – should receive the third Aliya. Apparently, the Shulhan Aruch held that since this Yisrael had been called to the Torah, he must accept the invitation and read. Therefore, even though a Kohen arrived and was given the first Aliya, the Yisrael must nevertheless remain and receive an Aliya, so that he will not be considered as though he refused an invitation to come recite the Beracha over the Torah.
This Halacha demonstrates the importance of receiving an Aliya, and the extent to which one must welcome this privilege. When a person is offered an Aliya he should not humbly decline; rather, he should eagerly embrace this opportunity to recite the Berachot over the Torah.
Summary: A person who is offered an Aliya to the Torah should not decline. This applies even in a case where a congregation called a Yisrael for the first Aliya because no Kohen was present, and a Kohen entered the synagogue before the Yisrael began reciting the Beracha. Although the Kohen in this case receives the first Aliya in place of the Yisrael, the Yisrael should remain by the Torah and is given the third Aliya, so that he is not considered as having refused an Aliya to the Torah.
