Ephesians 1:4: "according as He did choose us in him before the foundation of the world, for our being holy and unblemished before Him, in love" (YLT)
The Pulpit Commentary states: "The Father chose the heirs of salvation, selected those who were to be quickened from the dead (Ephesians 2:1) and saved, they [sic] chose them in Christ - in connection with his work and office as Mediator, giving them to him to be re-decreed (John 17:11, 12); not after man was created, nor after man had fallen, but 'before the foundation of the world.' We are here face to face with a profound mystery. Before even the world was founded, mankind presented themselves to God as lost; the work of redemption was planned and its details arranged from all eternity. Before such a mystery it becomes us to put the shoes from off our feet, and bow reverently before him whose 'judgments are unsearchable and his ways past finding out.'"
MY RESPONSE: Nevertheless, I believe that a number of exegetes today explain Eph 1:4 as applicable to a group of people, to wit, the elect--and not to individuals composing that group. In other words, God knows that some will accept His offer of salvation and others will reject it. But the Supreme One wills that all humans be saved and come to an accurate knowledge of the truth (1 Tim 2:4). Men and women are therefore not passive objects (pawns) in the divine work of salvation: we are free to choose God or spurn Him (Heb 3:12-14). Ergo, God, since He evidently knows all that it is possible to know, is aware that there is an indeterminately numbered group of persons who will respond to His free unmerited gift. So He either chooses not to know or knows as indeterminate the decision that men and women will make vis-à-vis His glorious Person and offer of salvation. My understanding of omniscience is consistent with that of Richard Swinburne who thinks of God in these terms:
"A person P is omniscient at a time t if and only if he knows of every true proposition about t or an earlier time that it is true and also he knows of every true proposition about a time later than t, such that what is [sic] reports is physically necessitated by some cause at t or earlier, that it is true" (Swinburne, 1977, 175).