The sermon focuses on Malachi 3:8-18, addressing the concept of tithing and offering from a perspective of trust and blessing rather than obligation. The minister emphasizes that when we give to God through tithes and offerings, we're not just giving money but investing in God's work and opening ourselves to His blessings. The message challenges the congregation to test God in this area and promises that He will prove faithful by opening the windows of heaven and protecting them from various forms of loss.