In The Name of Allaah, The Most Merciful, The Bestower of Mercy
Imaam As-Sadi [rahimahullaah] said: They [i.e. (the upright) scholars and teachers] are the mediators between the Messenger [sallal-laahu-alayhi-wasallam] and his Ummah with regards to propagation of his religion and clarification of his sharee’ah. Had it not been for these ones, the people would have been like cattle. They are the ones who guide the Ummah in the fundamental and subsidiary affairs of their Religion. They return them to the rulings pertaining to the rights and dealings that are incumbent upon a person to fulfil, just as they return them to the affairs related to acts of worship. Through them, the Book and the Sunnah are established; truth is distinguished from falsehood, guidance is distinguished from misguidance, the lawful is distinguished from the unlawful, good is distinguished from evil, and [sound] rectification is distinguished from corruption.  They are of varying ranks, in accordance with what they establish of knowledge, teaching and benefit- great or small. They have great rights [to be fulfilled] by the ummah and are possessors of a lofty status.

Therefore, the people must have love and respect for them. They must recognise their excellence and virtue, and thank them greatly. They are to supplicate for them in private and public, and seek nearness to Allaah by having love for them and praising them. They are to proclaim their excellence; guard the hearts [from harbouring evil against them] and [prevent] the tongues [from] insulting them, for this would tarnish their excellence. [End of quote] [Ref 1]

Shaikh Uthaymeen’s [rahimahullaah] explanation in Sharh Hilyati Taalibil Ilm:
Beware of the disease of the despots: (pride) [1]; for indeed pride, avarice and [blameworthy] envy were the first [sins] Allaah was disobeyed with. [2] So raising yourself above your teacher is pride [3]; and being arrogant towards the one who benefits you from amongst those who are below you [in knowledge] is pride; [4] and your falling short in acting upon knowledge is a sludge of pride and an indication of being deprived of [well-being]. [5]

[1] The Prophet said: Pride is to reject the truth and mock at the people.

[2] This refers to shaytaan’s behaviour when he was commanded to prostrate to Aadam, but pride prevented him from doing so. He refused and was haughty.

[3] Raising oneself can either be by way of the tongue [i.e. speech] and it can also be by way of sentiments [feelings, attitude, behaviour etc]. He [i.e. the student] might be walking with his teacher, whilst swaggering and saying: I did this and I did this.

[4] Likewise, being arrogant towards the one who is below you in knowledge is pride. This also occurs from some of the students. If someone below him in knowledge informs him of something, you find him arrogant and does not accept.

[5] We ask Allaah for wellbeing because from the types of pride is to not act upon the knowledge one knows. [Ref 2]

Ref 1: Source: Noorul Basaa-ir Wal Albaab Fee Ahkaamil Ibaadaat Wal-Mu-aamalaat Wal Huqooq Wal Aadaab, page: 57-58′ by Imaam As-Sadi (rahimahullaah). Abridged and slightly paraphrased]

Ref 2: Source: Sharh Hilyati Taalibil Ilm’ pages 38-40′ by Shaikh Uthaymeen [rahimahullaah]. abridged & slightly paraphrased