Although not obligatory, it is customary to recite several prayers at the end of Shaĥarit to conclude the prayer service by praising God and reinforcing our faith before beginning the working day. Additionally, since these prayers include verses from the Prophets and Writings, reciting them also counts as studying Torah. The composers of the prayerbook were aware that some people do not have a set time to learn Torah, so they added verses to enable people to fit in some Torah study too. The verses they chose are particularly apt in strengthening faith in God and the future redemption.
These prayers also include the chapter of Psalms (different for each weekday) the Levites recited in the Temple at the conclusion of the daily offering, and (in the Sephard version and in Israel) a description of the incense the priests offered in the Temple every morning and evening. Aleinu is recited towards the end of Shaĥarit, and at the very end of the Minĥa and Ma’ariv services. It is a powerful reinforcement of faith, and so it is customary to stand while reciting it.
