Ereunaō means to search diligently or investigate thoroughly — as one examines a text, explores a subject, or searches for a hidden treasure. In the New Testament it appears in John 5:39 (search the Scriptures), John 7:52 (search and you will find), Romans 8:27 (the Spirit searches hearts), 1 Corinthians 2:10 (the Spirit searches all things, including God's deep things), and 1 Peter 1:10-11 (the prophets searched carefully regarding the Messiah).
Two profound uses of ereunaō stand out. First, John 5:39 — Jesus tells His opponents, 'You study [ereunaō] the Scriptures because you think that in them you have eternal life. These are the very Scriptures that testify about me.' The searching is commended; but the result — missing the One the Scriptures point to — is the ultimate tragic irony of biblical literacy without transformation. Second, 1 Corinthians 2:10 reveals that the Spirit searches the bathē tou theou — the depths of God. The Spirit has access to the very interior of the divine being and communicates those depths to believers. The searcher of all things is given to those who believe.