What does the phrase 'in that day' mean in the Bible?

'In that day' is a phrase used repeatedly in Scripture, signifying a time designated by God for His divine action, particularly in revealing His salvation through Christ. This phrase appears over 40 times in Isaiah alone and encapsulates both God's sovereignty in planning and the believer's response to His grace. It marks significant events of salvation and divine visitation when God draws His people to Himself, leading them to a place of recognition, repentance, and ultimately praise. Every instance serves as a reminder that salvation is timely, purposeful, and unsolicited by human effort.