Brian Guerin emphasizes the urgency of spiritual readiness in 'The Last Hour Sifting,' urging believers to allow God to sift out the chaff in their lives to prepare for His return. He draws parallels between the sifting by God, which leads to holiness and purity, and the sifting by the enemy, which seeks to expose weaknesses and sin. Guerin highlights the importance of living a generous life, rooted in biblical principles, and warns against the dangers of clinging to sin and mixture, as exemplified by King Jehoram. He encourages the congregation to embrace the sifting process as a means of becoming a pure and powerful bride for Christ. The sermon concludes with a call to prayer for the Holy Spirit to cleanse and prepare the hearts of the believers.