In the prayer, the Muslim must say the Testification of Faith in Arabic by saying:  <<Ash-hadu alla ilaha illallah, wa ash-hadu anna Muhammadar-Rasulullah.>>) Since the Testification of Faith (the two shahadahs) is the foundational root of Islam, it is obligatory upon every Muslim know their meaning.

(The meaning of ash-hadu alla ilaha illallah), I testify that no one is God except Allah, (is: I know, I believe), i.e., I submit to and I accept in my heart (and I declare) with my tongue (that nothing is worshipped rightfully except Allah.) That is, nothing deserves to be worshipped except Allah.  The meaning of the term worship (al-^ibadah) in the Arabic language is the ultimate submission and subjugation of one to another, as stated by the linguist and Hafidh Taqiyyud-Din as-Subkiyy[1]. Thus, it is known that the term worship does not mean the mere obedience of one, calling upon one, seeking the help or aid of one, fearing one, or being hopeful of one, as some people think.

[1] He is ^Aliyy the son of ^Abdul-Kafiyy as-Subkiyy, Taqiyyud-din the father of al-Hasan, follower of the Shafi^iyy school. He was born in Sabkil ^Abid on the first of the Islamic month of Safar, year 638 Hijriyy (Safar 1, 638), and died, may Allah have mercy upon him, in the year 756 Hijriyy.  In “At–Tabaqat,” al-Isnawiyy said, “He [Taqiyyud-din as-Subkiyy] was one of the most insightful people we saw among of the People of Knowledge, and among the most comprehensive of them in different fields of knowledge, and among the most eloquent in precise matters, as well as being the most reputable among them in that.” Refer to Tabaqat Ash-Shafi^iyyah Al-Kubra, published by The House of Ihya’ al-Kutub al-^Arabiyyah (139/10), and Tabaqat ash-Shafiyyah authored by al-Isnawiyy, published by The House of al-Kutub al-^Ilmiyyah, 1^st Edition (350/1).