Genesis 17:18

And Abraham said before the Lord, May not Ishmael be established, and serve before Thee?

‘LU’ (O) THAT ISHMAEL MIGHT LIVE BEFORE THEE. The meaning of this word lu everywhere is as the word im (if), and it is also found combined in the word lulei, which means “if not.” [The Hebrew word lulei, ordinarily written with a yud at the end] is sometimes written with an aleph at the end., 43:10. It is also combined into the form of ilu, as in the verses: ‘Ve’ilu’ (But if) we had been sold for bondmen and bondwomen; ‘Ve’ilu’ (And if) a thousand years twice told. The purport of this word ilu is “even if,” and its meaning is as if it said, “if if,” the double use of the word being for the purpose of emphasis, as in the expressions: Is it only through Moses alone;) are redundant and used for emphasis. Was it because there were no graves; are both negatives. Again the redundancy is for special emphasis. and other similar cases. Abraham thus said: “If Ishmael live before Thee, I will be pleased with this blessing with which Thou hast blessed me, namely, with seed from Sarah.” For since He promised him at first, One born of your own body is to be your heir, and the heir was to be one person, he [Abraham] had thought that this referred to Ishmael. But now that he was told that he will beget a child from Sarah and he understood that this child was to be the heir, he feared lest Ishmael die. Therefore, he said this: [O that Ishmael might live before Thee].
Live before Thee. Rashi explained: “Live in reverence of Thee, similar in meaning to Walk before Me, which Onkelos renders, ‘Worship Me.’” But this is not correct, since He said, And as for Ishmael, I have heard thee. Instead, its meaning is that he live and his seed will always exist.

ויאמר ... לו ישמעאל, he meant to say that he would be content if Ishmael whom G'd had granted him, a gift he considered an extremem act of loving kindness on the part of g'd, would live a meritorious life, abiding by G'd's wishes. יחיה, a life in the full sense of word, that he would have children, would multiply and generally be an asset and a credit to his father. If Ishmael were to develop in this manner, G'd could keep his promise to Avraham to give the land of Canaan to his descendants. (compare 12,7) That prophecy would then be fulfilled by means of Ishmael.