In Chapter 1 of Heaven on Earth, Thomas Brooks argues that believers can attain a firm, well-grounded assurance of their salvation in this life, basing his claim on ten core biblical arguments. He demonstrates that assurance is built on universal gospel truths rather than private revelations, that scripture's primary purpose and promises are designed to foster certainty, and that God has placed internal "springs" of assurance—such as faith, hope, a good conscience, and love for believers—within every Christian. Furthermore, Brooks highlights that God actively commands the pursuit of assurance, provides practical means (like self-examination and the Lord's Supper) to reach it, and calls believers to constant spiritual joy, which requires knowing one's standing with God. Ultimately, he refutes theological systems that promote perpetual doubt, affirming that God's children can rest securely in His unchangeable love and covenant promises.