Philippians 1:6 - "I am sure of this, that he who began a good work in you will bring it to completion at the day of Jesus Christ." (ESV)
The basis for your change is God's promise, not your positive mental attitude. God has said that HE will complete what HE started in you. That's his promise.
2 Peter 1:4-8 says, "Through these he has given us his very great and precious promises, so that through them you may participate in the divine nature and escape the corruption in the world caused by evil desires. For this very reason, make every effort to add to your faith goodness; and to goodness, knowledge; and to knowledge, self-control; and to self-control, perseverance; and to perseverance, godliness; and to godliness, brotherly kindness; and to brotherly kindness, love. For if you possess these qualities in increasing measure, they will keep you from being ineffective and unproductive in your knowledge of our Lord Jesus Christ." (NIV)
The passage above is saying that because we have God's promises of walking in holiness, make every effort to add on goodness, knowledge, self-control, etc. Your effort is motivated out of God's love and his promise that you will mature.
God makes his promise, and then gives us a part to play in the fulfilment of the promise. This is how he works. God invites us into the process of personal character development. He is treating us as loved children, as valuable members of the family. He wants us to know that we can work with him to see his promise fulfilled in our lives.
God has promised that HE will finish what HE started in you. Will you join him?
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Created with images by carlosalvarenga - "men thinking man" • jniittymaa0 - "light bulb light halogen"