Jesus does not save us by grace and then ask us to work in our own strength to stay saved or to advance in the Christian life. We are saved in the power of God through Christ. We are sanctified (made spiritually mature) by that same power.
It is true that the path to true spiritual life is a narrow one but the “guardrail” which ultimately keeps us on that path is the unmerited favor of God in Jesus Christ, not our self-effort apart from Him.
A child of God must many times remember that the One who saved him is the One who sanctifies him. Our own attempt to start living the Christian life did not make us Christians, receiving the Son of God by grace through faith is what made us new creatures in Him.
That same grace-empowered faith is the source of our ability to authentically live out the Christian life until He returns or we go to be with Him.
…continue to work out your salvation with fear and trembling, for it is God who works in you to will and to act in order to fulfill his good purpose. Philippians 2:12-13 (NIV)
