Pastor Hardy's sermon "The Gospel Is Simple" focuses on the seed of the serpent, stressing the importance of trusting God's word and rejecting doubt and deception. He clarifies misconceptions surrounding this topic, refutes the belief of the serpent having relations with Eve, and explains that the seed of the serpent symbolizes not trusting God. The sermon highlights the consequences of disobedience by Adam and Eve, the lineage struggling with sin throughout the Old Testament, and the victory over sin through Jesus Christ's sacrifice and resurrection. Pastor Hardy encourages believers to live in alignment with God's word, work out their salvation, and find strength to overcome struggles through Christ.