John Gill emphasizes that the message from God, as revealed through Christ, is that God is light, symbolizing purity, holiness, and knowledge, devoid of any darkness or sin. This declaration serves as a promise that those who walk in the light will have communion with Him, while those in darkness will not. Gill explains that God, being light, illuminates the truth and is knowable through His creation and His Word, particularly through His Son. He stresses that God's nature is unchanging and perfectly holy, contrasting with the ignorance and sin found in humanity. Ultimately, the sermon calls believers to recognize and embrace the light of God in their lives.