Amidst the laws of Kriat Shema, Maran (author of the Shulchan Aruch) mentions (in siman 61:2; listen to audio for precise citation) a Halacha that emerges from a verse in Kriat Shema: "Asher Anochi Metzavecha Hayom" ("which I am commanding you this day"). Maran writes that one should recite Kriat Shema each day as if it is new to him. Generally, familiarity and repetition gradually lead to a degree of monotony; we normally do not get excited over experiences that we have each and every day. Maran therefore tells us that although we recite Shema every day, we must recite it with an attitude of freshness and novelty, with enthusiasm, as if we recite it for the very first time in our lives.
In his comments to this Siman (chapter), the Kaf Ha'chayim cites from Rabbi Chayim Vital (famous Kabbalist, Tzefat, 1543-1620) a fundamental notion concerning the essence of prayer. Rabbi Chayim Vital developed the idea that no two prayers are ever alike. Not only do the Shabbat and festival prayers differ – both in content and spiritual effect – from weekday prayers and from one another, but the weekday prayers themselves differ from one another. The effects of the Shacharit service on the upper worlds differ substantially from those of the Mincha and Arvit prayers. Moreover, no two Shacharit prayers are identical, either. Every time a person prays, he introduces a new quality to his prayer based on his intention and unique experiences, and the circumstances of that particular prayer. It therefore behooves us to realize each time we begin to pray that we are not reciting the same prayer we recited the day before. Rather than falling into the trap of heartless, mechanical prayer, we must recognize the unique power and significance of each and every prayer and each and every Keriat Shema, and recite them with feeling and emotion.
A Rabbi once applied this theme of "Asher Anochi Metzavecha Hayom" on a broader level to religious life in general. What this idea teaches is that one should approach his religious observance with the attitude of "one day at a time." People are often frightened by the lifelong commitment entailed by Torah observance; they feel they cannot possibly live up to the Torah's demands for so many years. Likewise, people tend to focus too heavily on mistakes of the past and wrongly conclude that they have already lost their chance at religious excellence. Judaism teaches us to focus our attention on that "which I command you this day." Rather than dwelling on the past or worrying about the future, we are to concentrate on today's obligations and responsibilities. Each Shacharit should be looked upon and treated as our first Shacharit, because our attention should be focused primarily on today's responsibilities, rather than our mistakes of yesterday or challenges of tomorrow.