because you will conceive and give birth to a son. No razor may be used on his head, because the boy is to be a Nazirite, set apart to God from birth, and he will begin the deliverance of Israel from the hands of the Philistines.” - Judges 13:5 NIV
It's interesting that the angel of the Lord didn't tell Manoah's barren wife that the son God was going to give her would be the deliverer of Israel, but that he would 'begin the deliverance of Israel from the hands of the Philistines'.
Deliverance is often not instantaneous. In my own life, it is usually only after years that I can look back and see that God was always in the process of delivering me from whatever oppressing circumstance I find myself in. That's the way God manifests his power, not that he can't do the miraculous instantaneously, but most often it's a steady, slow, progression towards deliverance that we experience.
We work on the area that needs deliverance, we achieve some success, and suddenly we find ourselves almost back at where we started, but not quite. We work some more, we fall back, we work, we fall. Then one day, we realize that we are free. Just as the Philistines power over Israel eventually faded into non-existence, the forces that hold sway over us fade away as God continues his work in our lives.
It was not the Israelites doing or our own actions that bring about change. It is always God's ultimate plan being carried out. As Paul wrote to the church at Philippi:
Being confident of this very thing, that he which hath begun a good work in you will perform it until the day of Jesus Christ: - Philippians 1:6 KJV
God begins our deliverance and he will be there until it is finished.