What does the Bible say about adoption as children of God?

In Romans 8:15-16, we see that believers receive not a spirit of slavery that brings fear, but a spirit of adoption, allowing us to cry out 'Abba, Father.' This communicates a profound relationship, transitioning us from slaves to beloved children of God. Even amidst our failures, the Holy Spirit testifies to our spirit that we are indeed God's children, a grace that is not based on our merit but on God's choice to adopt us into His family. This truth gives us the assurance to approach God confidently, regardless of our weaknesses or past sins.