וידבר ה' אל משה לאמור, "God spoke to Moses for him to communicate.⁠" According to the plain meaning of the text the word לאמור means that Moses was to relay the instructions received from God to the people. Alternatively, the word could mean that in addition to what the Torah has spelled out clearly for all to read and understand there are hidden meanings to be deciphered by those who apply themselves to Torah-study in depth. The נגלה, the revealed part, are the details of the commandment. The נסתר, the mystical, hidden aspect of this portion, is that which not everybody can grasp even if he tries. There have always been aspects of Torah not accessible to the average person. This is what David said (Psalms 62,12) "God has said one thing; yet I have heard two.⁠" A single communication may contain more than one message. Solomon echoed the same sentiment when he said: "a word spoken properly is like golden apples set in silver" (Proverbs 25,11). In this verse Solomon compared the matters which are revealed to silver, whereas matters concealed he likened to gold, i.e. they had first been overlaid, made invisible by silver.

The meaning of our verse as well as most verses which commence in a similar form is: God told Moses the commandment and implied that he should tell the Israelites about it. In addition, לאמור, he told Moses to reveal to the people the more profound aspects of the commandment, aspects which do not meet the eye of the reader.

Nachmanides writes in his commentary on Exodus 6,10 (where the verse commences in the same manner as here) "the word אמירה refers to a complete utterance, meaning that an אמירה נראית, 'a superficial utterance'" is not sufficient. [Nachmanides tries to justify why sometimes God added "say to the Children of Israel,⁠" whereas other times He contents Himself with the word לאמור alone. Ed] Seeing that the quality of God's communications to Moses was so superior and clearer than His communications to lesser prophets, God was able to say to Moses: "make the matter clear to your listeners the Jewish people.⁠" Other prophets (Numbers 12,8) with whom God Himself spoke in riddles were not able to clarify matters to the people in the degree Moses was able to clarify it for them.

A Kabbalistic approach: The words וידבר ה' אל משה reflect the inner force, the concealed force, the word לאמור is a reference to the fact that this force had become manifest by means of the Shechinah. This is the meaning of the words in Exodus 24,12 אשר כתבתי להורותם, "which I wrote to teach them.⁠" The word להורתם is written defective, without the letter ו which should be part of the plural ending, thus making it similar to Song of Songs 3,4 ואל חדר הורתי, "into the bedroom of my parents.⁠" This is merely a euphemism for the acquisition of information reserved for the intimates of God.
You are aware already that the expression דבור is a deeper form of communication than אמירה. Whereas אמירה describes the oral Torah, דבור describes the written Torah [with its multifaceted ways of interpretations. Ed.] The experts of Kabbalah were thoroughly familiar with this. This is what prompted Eicha Rabbah to translate the words בצע אמרתו In Lamentations 2,17 as בזע פרפורין שלו, "He tore His purple curtain (allowed the Temple curtain to be destroyed).⁠" [The standard translation of the words is: "He carried out His decree.⁠" Ed.]
We have to ask ourselves what made the author of this Midrash translate these words in this fashion? The word אמרא, as cloak, i.e. or better "a fringed garment,⁠" is well known. In this instance the word פרפורין may be understood as a euphemism for the edge of such a cloak. Our sages understood the verse in Lamentations as explaining the reason why the Temple was destroyed. First the Jews had despised the תורת ה' צבאות (Isaiah 5,24). This was a reference to the written Torah. Then (same verse) ואת קדוש ישראל נאצו, "and the Holy One of Israel they spurned.⁠" This is a reference to the oral Torah.
To get back to our verse here. The word ויאמר or לאמור is derived from אמרא, the edge of a cloak a person wears on his left side. We have a verse in Samuel I 28,14 illustrating this: "he is wrapped in a cloak.⁠" We also have a verse symbolically depicting God Himself as wrapped in such a cloak, i.e. עוטה אור כשלמה, "He wraps light around Himself as a man would wrap a cloak around himself" (Psalms 104,2). The cloak referred to in that verse is the attribute of Justice. On the other hand, the word דבור, and therefore וידבר, when employed by the Torah is derived from the word דבורה, the bee, which though providing honey, i.e. sweetness, also harbors a deadly sting. The bee therefore symbolizes an attribute of God which combines both the attribute of Mercy and the attribute of Justice. The oral Torah is emanated from that attribute, seeing it is a derivative of the written Torah and the written Torah itself is based on the combination of the attribute of Justice and the attribute of Mercy.