Genesis 16:13

And she gave thanks before the Lord whose Word spake to her, and thus said, Thou art He who livest and art eternal; who seest, but art not seen! for she said, For, behold, here is revealed the glory of the Shekina of the Lord after a vision.

ותקרא שם ה, the meaning of the words ותקרא שם ה', is prayer. It refers to the kind of prayer in which one praises the Lord, or thanks Him. This prayer may be offered silently, in one's mind or with words. The source for this definition is found in Berachot 32: "as a rule a person should first address G'd by praising Him, before beginning to pray." [to tell G'd of his requests from Hi. Ed.] This thought is reflected in the inscription in most synagogues on the Holy Ark שויתי ה' לנגדי תמיד, "I am ever mindful of the Lord's presence" (Psalms 16,8) The word קרא for prayer is also found in Lamentations 3,55 קראתי שמך ה', "I have prayed to You o Lord," as well as in Psalms 79,6 ושמואל בקוראי שמו, "as well as the prophet Samuel who would pray (successfully) to Him." Also the well-known line כי שם ה' אקרא, (Deut. 32,3) is best translated as "for I will pray to the Lord," rather than as "I will proclaim the name of the Lord." Hagar's new insight, expressed by her saying אתה א-ל ראי, meant that whereas up until now she had assumed that revelations from G'd are confined to the house of Avram, she had now learned that G'd may reveal Himself in any location. This is in line with Baba Metzia 59 כל השערים ננעלו חוץ משערי דמעות, that although the gates of prayer have largely remained shut since the destruction of the Temple, the prayer of people complaining (shedding tears) of being dealt with unfairly by their fellow human beings have not been closed.

ותקרא, the reason why Hagar called G'd א-ל ראי, was that she oly realized in retrospect that she had been addressed by an angel, i.e. by an angel who brought her G'd's message. She had not previously believed that a human being could behold an angel with her physical eyes, a lesson also learned by Manoach in Judges 13,22. As soon as she notice how this messenger who had appeared to her in human garb disappeared in less time than it takes to blink an eye, she knew that that being had been an angel and she called out "you are the angel who manifests G'd's presence." She meant that she had seen a Divine being that is capable of being perceived as such by man. The construction "ro-i" is similar to the construction "o-ni" in Lamentation 3.1 or in "do-mi" in Psalms 83,2, or in Genesis 43,11, "tzo-ri."

כי אמרה, she had said in her heart "I recognize that he is an angel, for when a human being departs from the presence of another human being the one remaining behind can continue to see the one departing for a considerable time until he recedes into the distance. I, however, have been unable to see a trace of this being even הלום, when he was still close to me, ראי, had seen me, i.e. the being who had revealed himself to me. It is clear to me therefore, that this must have been an angel, i.e. a disembodied creature."

The word ראי means "the one who sees me."