Kommentar zu Bereschit 16:11

הנך הרה BEHOLD THOU WILT BE WITH CHILD — when you return you will conceive, just as the same phrase הנך הרה (Judges 13:7) spoken of the wife of Manoah (where it certainly appears to be thou wilt conceive in the future).

AND THOU SHALT CALL HIS NAME ISHMAEL. The angel informed Hagar that his name will be Ishmael — just as in the verse, Behold, a son shall be born unto the house of David Josiah by name³⁶⁰I Kings 13:2. — and he told her that she should so call him, and thus remember that G-d heard her affliction.³⁶¹The name Ishmael (G-d heareth) is, as the angel explained to Hagar, “because the Eternal hath heard thy affliction.” (Verse 11.) Now Abraham either called him by this name on his own,³⁶²Verse 15: And Abraham called the name of his son, whom Hagar bore, Ishmael. with the intent that G-d hear him and answer him, or the Holy Spirit rested upon him, as Rashi has it, and he called him Ishmael because G-d had heard his mother’s affliction, as the angel had said.
The correct interpretation appears to me to be that the angel commanded Hagar that she call him so, but she, being a concubine,³⁶³Verse 3 above is no proof to the contrary, as it may express only Sarai’s desire. was afraid to give a name to her master’s son, so she revealed the matter to him, and Abram fulfilled the word of G-d. Scripture, however, did not need to delve at length into this matter.

ויאמר ... הנך הרה, the angel used these words as an introduction, seeing he was well aware that Hagar knew that she was pregnant as the Torah had reported in verse 4, as well as Hagar's reaction. The message that angel had come to deliver was וילדת בן, "you will give birth to a son." The word יולדת is a composite composed from the word וילדת, which is a verb in the past tense converted into the future tense by the letter ו at the front, the other component being the word ויולדת, the same root as a present participle. The meaning of the combined composite is that seeing that the birth was something that had not yet occurred, the verb must contain an allusion to the future, whereas seeing that Hagar knew that she was pregnant, i.e. that the process which would result in a birth had already begun, the formulation of the verb had to reflect this fact also. The angel's message was: "just as you are aware that you are pregnant you should be equally aware that you will bear a son as a result of this pregnancy." There are some grammarians who believe that the root of the word here is similar to a four-lettered verb.