The word "Deen" (anglicized also as "Din") (religion) is an Arabic term which technically means "belief in a creator for the universe and man as well as in instructions consistent with this belief."[1] Keeping in view this definition and the technical explanation of "Deen", it is clear that every religion consists of two parts:
1. Beliefs or tenets that are fundamental to it and which are treated as the basis and roots of the religion.
2. Instructions or codes of practice being consistent with those fundamentals and ideological basis.[2]
The phrase "Principles of faith" or "Roots of Religion" is applied to the first part (beliefs) and the phrase "Branches of Religion" is applied to the second part i.e. the practical laws.[3]  The Principles of faith are called principles because they relate to the thoughts and beliefs which serve as the basis and pillars of faith. Thus, the way and how an individual gives attention to the branches of religion largely depends on how profoundly and strongly he believes in those principles.[4] The principles of religion have two general and specific applications or meanings. The principles of religion when used against the practical laws of the religion is the general application or the common and widespread meaning and when it is used in the sense that it includes one or more ideological principles which characterizes a certain religion (in addition to the principles of religion in the general sense) is the specific application and meaning. [5]
The principles of the religion of Islam in their general senses include monotheism, prophethood and resurrection. The principles of religion in their specific sense (principles of a specific religion) include not only those three principles but also justice and imamate (leadership).  With that said, it is now clear as to what principles of religion mean and where they are applied. Also, it is learned that the branches of religion refers to the practical laws. The principles of religion that have to do with one's own knowledge and insight about basic tenets of the religion precede the branches of religion which are concerned with practice. That is to say, insofar as there is no knowledge and belief, practice has no meaning. Of course, knowledge in the principles of beliefs is not mere knowledge; rather it is knowledge twixt with certainty.
Late Faiz Kashani (ra) says in this regard: "The best among these two (knowledge and practice) is knowledge; knowledge is the tree and worship is the fruit of the same."[6]
Also, when it comes to the relationship between knowledge and belief (certainty), he says: "Belief is based on knowledge because belief is to confirm something. It requires assuming something which is the very knowledge. Knowledge is presupposed and is the prerequisite.  Belief is proportionate to knowledge.[7]
Hence, the principles of religion are those principles which man should first understand with his own knowledge and insight so as to enter Islam. Thereupon, he will see the practical laws of Islam in front of him.[8]   Since acquiring knowledge precedes worship[9] and knowledge is superior over practice, therefore, such matters are described as "principle".   After entering the religion of Islam, he encounters a number of devotional and practical duties (such as the external deeds like prayers, zakat, fasting etc. and internal ones such as tavakkol, piety, gratitude etc…) [10]which are technically called as the branches of religion. But as was clarified, the term "branches of religion" is in no way in opposition to an act of worship being part of the pillar of faith. If we consider Islam to be like a house, these principles are the entrance to the house. Obviously, the house has pillars which the house is based upon.  Such statements do exist in the Islamic textual sources from the Ahlul-Bayt (AS) about some acts of worship. Imam Baqir (AS) says: "Islam is based on five pillars: Prayer, zakat, Hajj, fast, Hajj and wilayah." In response to Zurarah, he said: "Wilayah is the best of these pillars."[11] These five acts of worship and others become meaningful only when man enters Islam. In a narration reported from Imam Sadiq (AS), the imam makes references to the status of knowledge and then action. The Imam (AS) says: "The best deed with which a man may attain divine proximity is knowledge followed by prayer."[12] Yes, indeed, the prayer is very important, so much so that it has been described as the pillar of faith[13]. Imam Baqir (AS) says: "If one's prayers are accepted on the Day of Judgment[14], the rest of deeds are also accepted and if prayer is rejected, the rest of religious deeds are also rejected.[15] But this extraordinary importance is not in opposition with the prayer being a branch of faith.

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