In Pastor Josh's sermon "Remember What You've Learned," the focus is on recalling the core teachings of the gospel from 2 Peter 1:12-21. He emphasizes that our life experiences and wisdom gained are invaluable in understanding God's truth and shaping our faith. Using examples like relationships and personal growth, he explains how our experiences teach us valuable lessons. Peter's example is cited to encourage recalling the gospel's core teachings for spiritual growth and passing them on to future generations.