A.B. Simpson emphasizes the importance of counting all experiences as joy, regardless of our feelings. He explains that the act of 'reckoning' is crucial, as it involves treating ourselves as dead to our old nature and choosing to rejoice in faith. Simpson encourages believers to fix their hearts on God and to develop a habit of rejoicing, which leads to a spirit of gladness and praise. He reminds us that even in times of hardship and lack, we can still find joy in the Lord, as our peace comes from knowing Jesus is in control. Ultimately, the sermon calls for a steadfast commitment to joy and faith amidst life's challenges.