Moses ben Nahman (מֹשֶׁה בֶּן־נָחְמָן - "Moses son of Nahman"; 1194–1270), commonly known as Nachmanides and also referred to by the acronym Ramban, was a leading medieval Jewish scholar, Sephardic rabbi, philosopher, physician, kabbalist, and biblical commentator. He was raised, studied, and lived for most of his life in Girona, Catalonia. He is also considered to be an important figure in the re-establishment of the Jewish community in Jerusalem following its destruction by the Crusaders in 1099. This is a letter he wrote to his son”
Let your words be spoken gently; let your head be bowed. Cast your eyes downward, and your heart heavenward; and when speaking, do not stare at your listener. Let all men seem greater than you in your eyes: If another is more wise or wealthy than yourself, you must show him respect. And if he is poor, and you are richer or wiser than he, consider that he may be more righteous than yourself: If he sins it is the result of error, while your transgression is deliberate.
In all your words, actions and thoughts -- at all times -- imagine in your heart that you are standing in the presence of the Holy one, Blessed is He, and that His Presence rests upon you. Indeed, the glory of the Almighty fills the universe. Speak with reverence and awe, like a servant who stands in the presence of his master. Act with restraint in the company of others: If one should call out to you, do not answer with a loud voice, but respond gently -- in low tones, as one who stands before his mentor.
Take care to always study Torah diligently so that you will be able to fulfill its commands. When you rise from study, ponder carefully what you have learned; see what there is in it which you can put into practice.
Review your actions every morning and evening, and in this way live all your days in repentance.
Cast external matters from your mind when you stand to pray; carefully prepare your heart in the presence of the Holy One. Purify your thoughts, and ponder your words before you utter them.
Conduct yourself in these ways in all your endeavors for as long as you live. In this way you will surely avoid transgression; your words, actions and thoughts will be flawless. Your prayer will be pure and clear, sincere and pleasing to God, Blessed is He...
Read this letter one a week and neglect none of it. Fulfill it, and in so doing, walk with it forever in the ways of the Almighty, may He be Blessed, so that you may succeed in your ways and merit the World to Come that lies hidden for the righteous. Every day that you shall read this letter, heaven shall answer your heart's desires...