Maimonides gives us a very deep idea about the soul which is a sound piece of advice for life. Let’s first examine what straightness and truth are then we’ll understand what Maimonides instructions are.
The Talmud relates that Rabbi Safra was in the middle of reciting the Shema and someone came over to him and wanted to buy an item from him. As Rabbi Safra was saying Shema he was forbidden to even hint to the person whether or not he would sell it and certainly he could not negotiate with him. So Rabbi Safra ignored him. The man thought his offer was being ignored and he started offering more money for the item. Rabbi Safra continued to ignore him and the man kept on going higher and higher in price.
When Rabbi Safra finished reciting the Shema he said, “I’ll sell you the item” and the man took out his wallet to pay the highest last price he offered. Rabbi Safra said: “No, I want you to pay me your initial offer for in my heart I already agreed to it and I just was unable to talk as I was in the middle of reciting Shema. The verse says “He speaks truth in his heart”. My heart wanted the original price but you didn’t know that and kept on offering more. But the truth is I agreed to the lowest price and that’s what you should give me.”
This is the greatness of someone who sticks to the truth to the nth degree. You’d think he lost money on this transaction but in reality such a person who is totally honest with himself gained happiness in his life, calmness and being just. He is whole with himself and with his surroundings, he is a just person. He is true to the values he has inside and because of that all his outside actions are calm and happy. This is what “his inside like his outside is”.
Since he acts in a manner true to his values of justice and truth his inside is happy and calm as he doesn’t live with internal conflict. His inside and outside are one and the same.