The letter from Ramban
Listen, my son, to your father’s instruction and do not neglect your mother’s Torah (Proverbs 1:8).
Acquire the habit of always speaking calmly to every person at all times. And by this you will save yourself from anger, a serious character flaw that causes people to sin. As our Rabbis said (Nedarim 22a): Whoever is quick to anger, all kinds of hells (Gehinam) reign over him, as it is written (Ecclesiastes 12:10), “Put anger away from your heart and put away evil from your flesh.” “Evil” here means Gehinam, as we read (Proverbs 16:4): “...and the wicked are destined for the day of trouble.”.
Once you have been saved from wrath, the quality of humility will enter your heart. This quality is the best of all admirable traits (see Avodah Zarah 20b), because (Proverbs 22:4), “Following humility comes the fear of God.” Through humility, the quality of the fear of God will also enter your heart. It will cause you to always think about (see Avot 3:1) your origin and your destiny, and that while you are alive you are always like a worm, and the same after your death.
It will also remind you of Whom you will be judged before, the King of Glory, and it is written (1 Kings 8:27; Proverbs 15:11), “Even heaven and the highest heavens cannot contain you”—“How much less the hearts of men!” It is also written (Jeremiah 23:24), “Do I not fill heaven and earth?” says God.
And when you think of all these things, you will fear your Creator and guard yourself against sin, and with these qualities, you will be content with your portion. And when you act humbly, are ashamed of all men, fear them, and guard yourself against sin, the spirit of the Shekhinah, the radiance of His glory, and the life of the World to Come will rest upon you. And now, my son, understand and observe that whoever prides himself in his heart over creatures is rebelling against the Kingship of God, for he is worshiping himself with the garments of the kingdom of Heaven, as it is written (Tehillim/Psalms 93:1), “The Lord reigns; He clothes Himself in garments of splendor.”.
And what should one be proud of? Is it wealth? God makes one poor or rich (1 Samuel 2:7). Is it honor? It belongs to God, as we read (1 Chronicles 29:12), “Wealth and honor come from You.” So how could one adorn oneself with God’s honor? And someone who prides themselves on their wisdom surely knows that God “takes away the speech of the talkative and thwarts the reasoning of the wise” (Job 12:20)!
So we see that everyone is equal before God, for in His anger He humbles the proud, and when He wills, He raises up those who are low. So humble yourself, and God will lift you up! Therefore, I will now explain how to always behave humbly.
All your words will be kind, your head bowed, your eyes looking down, and your heart focused upward. Do not look at the face of the person you are speaking to. Consider everyone as greater than yourself. If he is wise or rich, you must show him respect. If he is poor and you are richer—or wiser—than him, consider yourself more guilty than he is, and that he is more deserving than you, since when he sins he does so by mistake, while you do so deliberately!
In all your actions, words, and thoughts, and at all times, consider in your heart as if you were standing before God, with His Shekhinah above you, for His glory fills the whole world. And your words will be with fear and awe, like a slave standing before his master. Be ashamed before the whole world.
When someone calls you, do not answer loudly, but gently and softly, like someone standing before their master.
Always take care to study the Torah diligently, so that you may be able to fulfill its commandments. When you rise from your study, reflect carefully on what you have studied, so that you may see what in it you can put into practice.
Examine your actions every morning and every night, and in this way, all your days will be filled with teshuvah (repentance). Focus on your prayers, removing all worldly worries from your heart. Prepare your heart before God, purify your thoughts, and think before you speak.
And so you will do all the days of your vain life and you will not sin. In this way, all your words, actions, and thoughts will be righteous, and your prayer will be pure, clear, clean, devout, and acceptable to God, for as it is written (Psalms 10:17), “When their heart is directed to You, hear them.”.
Read this letter at least once a week and do not neglect any aspect of it. Follow its instructions, and in doing so, walk with it forever on the paths of God, Blessed be He, so that you may succeed in all your ways.
Thus you will succeed in all your ways and merit the World to Come, which is hidden for the righteous. And each day you read this letter, Heaven will always answer according to the desires of your heart. Amen, Selah!