There's an almost unperceivable line between our choice of action in life and God's willingness to intervene. I say willingness, because as we know, God is capable of intervening in our lives, and indeed often does, but our perception is perhaps blurred by our obstinacy and lack of focus.
There are many Biblical records of God intervening in the lives of people in order to nudge them, or "encourage" them, in a certain direction.
Jonah disobeyed God when asked to go to Nineveh, (Jonah 1:1 onwards), and he was thrown in the sea and swallowed by a whale which then deposited him on dry land where he decided to go to Nineveh.
Paul persecuted the early-Christians and was thrown off his horse on the way to Damascus and eventually went on to preach about Jesus in many lands, even though he himself had never met Jesus personally. (Acts 8:1 onwards).
The Angel asked Mary to become the Mother of Jesus and she agreed. He also told Joseph not to abandon Mary but to take her as his wife. Later he announced the birth of Jesus to the shepherds, he also told the Magi to avoid going back to Herod, and warned Joseph to escape with Mary and Jesus to Egypt.
All these are examples of God's interventions in peoples' lives and people responding accordingly. No doubt you can think of many other such instances.
One thing should be clearly understood, however; in all these instances the individuals concerned had the right and the freedom to say "No" to God's invitation. Admittedly, you would think that being swallowed by a whale, or thrown off a horse and blinded, would be incentive enough to obey God; but it should be clearly underlined that at all times the choice to say, "No, I cannot do as you ask God" was present as an option.
Paul could have said, “All right God, I’ll stop persecuting Christians, but I’ll leave it at that.” He did not have to become one of the greatest missionaries ever and suffer many arrests, beatings and imprisonments and death for spreading the Good News of Christ. He did that voluntarily and was in no way forced by God into this course of action. The same applies to Jonah, Moses, Peter and the other disciples and to everyone else who chooses to follow Christ ever since. Including you and me. We are in no way forced to love and obey God. And many today choose not to.
Mary could have said, "No!", but she didn't. Joseph equally could have decided to leave Mary, but he didn't.
The principle that individuals at all times have a choice is paramount, because without it it would imply that God has created a robotic humanity unable to decide for itself and controllable by one Divine mind.
This principle applied then as it still applies now to you and me and many others.
If we are honest with ourselves, there have been several instances in our lives where God has intervened and "nudged" us in certain directions. Whether we answered the call or not is a personal matter. There have also been instances where His intervention has saved us from unimaginable bad situations; perhaps without our knowledge at the time, but thinking back we can see His hand in events in our lives.
What is important is to remember that God's interventions are like that of a friend. He advises on the best course of action, on what to do or say and when to do it; but at all time we retain the freedom of choice whether to accept the advice or not. Just as you would do if a human friend gave you advice on a certain course of action.
And that is the Thin Line of intervention upon which our faith depends.
God the loving Creator Father guides His creations through the teachings of Christ and the works of the Holy Spirit. We retain the choice as to how we respond.