‘As-Siraatul-Mustaqeem’ is a straight path with no sign of crookedness. It is the clear path of Islam which is like a highway among hundreds of streets; the creed that is moderate, free of the harms of extremism (exceeding limits) and negligence (disregard of limits).

Nawaas bin Sim’aan narrates that the Prophet (sallallaahu alayhi wa sallam) said, “ Allaah quotes a parable (of Islam such): A straight path with walls erected on either side. Both walls have several open doors that have curtains draped over them. At the entrance of the straight path someone calls out, ‘O people! Enter the straight path all together and do not opt for crookedness.’ Above the path, another caller warns every person who advances to open any one of those doors saying, ‘Woe unto you! Do not open it, for if you will open it you will enter it.’ So the straight path is Islam; the walls are the boundaries of Allaah; the open doors are the things that Allaah has forbidden; the caller at the entrance of the path is the Book of Allaah; and the one from above is the adviser Allaah has appointed in the heart of every believer.”

Every path is distinguished from others courtesy of those who follow it. In the Qur'aan, Allah Ta'ala elaborates on the straight path by speaking of it's distinguished followers.

“Whosoever obeys Allaah and the Messenger, then such people are the ones Allaah blesses; namely, the prophets, the siddiqeen (truthful), the martyrs, and the righteous.”
Mufassirul Qur’aan’ Abdullaah bin Abaas (radhiallahu anhu) says, “those who have been blessed with Your obedience and worship; namely, the angels, the prophets, the siddiqeen, the martyrs, and the righteous.”
To understand this better, know that those who are accepted in the court of Allaah are categorized in four ranks.
The first and highest is the rank of the prophets.
The second is the rank of the Siddiqeen; those who have the highest position from amongst the Ummah (nation) of the prophets; who possess spiritual excellence; better knows as Awliyaa (saints).
Third in rank are the martyrs, whose love for their Deen inspires them to even sacrifice their lives for the sake of it.
The fourth is the class of the Sulahaa; those who follow the Shariah (Islamic code of law) in totality; commonly known as the righteous ones.
The path followed by these four categories is the straight path. Attributing the straight path to these people teaches us that although the Qur’aan and books of Ahaadeeth are replete with guidance and knowledge of Deen, it is incumbent that one frequents the gatherings of to such people to learn from them and seek their advice, because guidance cannot be attained by merely reading religious books, or studying a translation of the Qur’aan. It is absolutely essential that one take on such a person as his mentor and guide.

On the other hand, Allah also warns us of the factors that would cause to stray from the straight path. Allah mentions that deprivation from the straight path is caused by one of two reasons.
Some people are deprived of being blessed with the straight path because despite having knowledge of the Shariah, they oppose it purely by reason of their wicked ways or base desires. In other words, they fall short in carrying out the commandments of Allaah , and as a result invite His wrath. They forsake their Religion for the temporary and lowly pleasures of the world.
Others adopt the wrong path due to lack of knowledge. Such people are the deviated ones who are unaware of the limits stipulated by Shariah. Consequently, they fall prey to extremism.

And: This is My path that is straightforward. So, follow it, and do not follow the 'subul' (other ways), lest they should make you deviate from His way. This is what He has enjoined upon you, so that you may be God-fearing.” (Al-An'aam, 153)

Based on a narration from Sayyidna 'Abdullah ibn Mas'ud (radhiallahu anhu): Allah be pleased with him, there is a report in Musnad of Darimi which says: 'Once the Holy Prophet (aallallahu 'alayhi wasallam) drew a vertical line and said: "This is the path of Allah." Then, he drew other lines on its right and left and said: "These are subul" (that is, the ways following which has been prohibited in this verse) and, then, he said: "Set upon every one of these ways there is a Shaytan who, after enticing people away from the straight path, welcomes them to this" (the ways under the charge of Shaytan, as shown in the drawing). After that, as proof, he recited this verse (153).'

It is said in Tafsir Mazhari that the purpose of sending the Qur'aan and the Prophet of Islam (sallallahu 'alayhi wasallam) is to make people subordinate their ideas, intentions and proposals to the Qur'an and Sunnah and cast their lives into the blessed model offered by him. But, what is happening is that people are bent on moulding the Qur'aan and Sunnah into the frame of their ideas and proposals. As a result, an Ayah of the Qur'an, or a Hadith of the Prophet (sallallahu 'alayhi wasalla) which does not meet their fancy, or is found to be contrary to what they would like it to be, would become the target of their so-called interpretation until it fits into the mold of their desires. This is the starting point from where other ways which leade people astray emerge - ways which throw them in doubts and innovations in the established religion (shubhaat and bid'aat). These are the ways from which people have been instructed to stay away in this verse.

In a nutshell, the path of genuine believers consists of knowledge of the true religion coupled with conformity to it. Hence, we should ask Allaah to protects us from the path who those who follow their base desires and are negligent of their Deen; and also from the path of the ignorant and deviated who have exceed the limits specified by Shariah. We should pray that Allaah shows us the path between these two extremes, which is pure of misgivings and erroneous beliefs.

May Alla Subhaanahu wa Ta'aala safeguard us, our families, and the Ummah at large. Ameen