How do we know that salvation is according to God's purpose and grace?

In 2 Timothy 1:9, it states that God 'saved us and called us with a holy calling, not according to our works, but according to His own purpose and grace.' This underscores the belief in sovereign grace, emphasizing that salvation is initiated by God, based solely on His divine purpose. Additionally, Ephesians 1:4 reveals that God chose us in Christ before the foundation of the world. This pretemporal choice demonstrates God's sovereignty in salvation, showing that it is not dependent on human works or merit but rather on God's will and grace, which transcends time and circumstances.