A Song of Degrees
שיר למעלות אֶשָּׂא עֵינַי אֶל-הֶהָרִים מֵאַיִן יָבֹא עֶזְרִי: עֶזְרִי מֵעִם יְהוָה עֹשֵׂה שָׁמַיִם וָאָרֶץ:אַל-יִתֵּן לַמּוֹט רַגְלֶךָ אַל-יָנוּם, שֹׁמְרֶךָ: הִנֵּה לֹא-יָנוּם, וְלֹא יִישָׁן שׁוֹמֵר יִשְׂרָאֵל: יְהוָה שֹׁמְרֶךָ יְהוָה צִלְּךָ עַל-יַד יְמִינֶךָ: יוֹמָם הַשֶּׁמֶשׁ לֹא-יַכֶּכָּה וְיָרֵחַ בַּלָּיְלָה: יְהוָה, יִשְׁמָרְךָ מִכָּל-רָע: יִשְׁמֹר, אֶת נַפְשֶׁךָ. יְהוָה יִשְׁמָר-צֵאתְךָ וּבוֹאֶךָ מֵעַתָּה וְעַד עוֹלָם.
Explanation For The blessing
"A Song of Degrees" is the general title of Psalms 120-134. These psalms are unique in their emphasis on Jerusalem, the Temple, its rituals, and the motif of divine providence. The 'degrees' refer to the stairs of the Temple, as the Levites would recite these psalms during the ascent.
"A song of degrees: I will lift up mine eyes unto the hills" is considered a cry and a plea and is recited in times of trouble. Psalm 121 is often said for the sick and during the evening prayer service. The song was sung when the Levites began to ascend, alluding to the ascent of the righteous from the tree of life to the honorable chair.
The psalm deals with one of life's most essential questions, collectively and individually, as it asks "from whence cometh my help"? From whence will our salvation come? However, that "help" pertains mostly to Tikun Olam (the repairing of the world) and Tikun HaNeshama (the repairing of the soul) that will allow us to reach the "degrees" of the world to come. Our world is strewn with obstacles and is essentially unrepaired, thus requiring "help".
Hence, this psalm should be invoked with great intent whenever one is in need of assistance / redemption, and God shall answer.