How do we know that the concept of God's promises is true?

God's promises, such as those made to Joshua, reflect His unwavering faithfulness and are ultimately fulfilled in Christ. In Joshua 1:3-4, God assures Joshua of victory and success, a promise that extends to all of God’s people through Jesus. Ephesians 1:3 reinforces this by declaring that believers are blessed with all spiritual blessings in Christ. Hence, our assurance of God's promises comes from Christ's succeeded work and our being united with Him, affirming that all God intends for us is found in Him.