From Dennis F. Kinlaw's "Let's Start With Jesus: A New Way of Doing Theology":
Scriptural Evidences of the New Birth: Titus 3: 4-7 (Holy Spirit initiates a new life within us, the very life of God), Rom. 5:8 (Holy-love of God poured into our hearts), IJn. 3:1, 11 (tyranny of self-absorbtion broken, the love we receive from God is lavished upon others). Proof of this change 2-fold- We experience a consciousness of reconciliation with and belonging to the Father again (Rom 8: 15-26, IJn. 3: 1-2) and experience change in conscious concerns, a divine love for God and Man (2Cor. 5:14-15). We are to walk (keeping in step, walking) in the Spirit (Gal. 5:25); it is the Spirit we live by, not the flesh- (Gal. 2:20, Phil. 1:21, 1Cor. 4: 16-17).
It is possible for disciples to have an undivided heart (sanctification): Dt: 30:6, Mt 5:8, Mk 12: 28-34, Rom 6: 1-4, 8: 1-15, 12: 9-15, 13: 8-10, 1Cor. 12:3, Phil. 2: 1-11, 2: 19-23. (Compare the verses in Phil. to Phil. 1:17 and Rom. 2:8- these verses indicate that a believers love can be tainted by selfishness. The word for self seeking in both these verses is eritheia). Paul demonstrates how he looked out for the interests of others: 1Cor. 3: 3-9, 8: 9-13, 9:12, 15, 18-19, 22-23, 10: 31- 11:1, 15: 1-6. See also 1Jn. 1:7. Paul begins Rom. by boasting of the Gospel's power to save; at the close of Rom. ( Rom. 12-15)Paul demonstrates how salvation works itself out in a disciple's life. Rom 12:1-2, Paul speaks of a New Testament sacrifice, not of animals, but of self. The grace that God gives in response to this self-sacrifice is the agape of God which is other oriented: Rom. 12: 3-5, 10, 14-20, 13: 4, 13: 1-7, 8-10, 14: 7-8, 15: 1-3, 23-32. This is not a state obtained in our own strength: Gal 2:21. The Spirit works through faith: Gal: 5:6.
Why do we need sanctification in addition to salvation? Only after we walk with Jesus in intimate fellowship for a while do we realize the fullness of our sinfulness. The Holy Spirit reveals this to us. We must trust the Lord to do this and that it is for our eternal good. Failure to trust God in this is the final evidence of our sinfulness. (1Jn. 4: 18.)