Isaiah 48:5 explains God declared future events beforehand so people wouldn't credit idols — Jesus warns beforehand to prevent deception by false christs.

John 16:1 reveals Jesus' purpose in forewarning: to prevent disciples from falling away—directly echoes 'told you beforehand'.

In John 13:19, Jesus also says He tells before it happens so that when it occurs, they may believe He is the Messiah.

In John 14:29, Jesus repeats the same purpose: foretelling so that belief may follow when events unfold.

In John 16:4, Jesus again says He has told them so they will remember when persecution comes.

Ezekiel 3:21 emphasizes warning the righteous to save them—parallels Jesus' purpose in telling disciples beforehand.