Where you say, “Rather, it is by this word preached that I have the Holy Spirit working in me, causing me to turn to God”, it’s worth being aware that – far from moving from the Lutheran to the Calvinist view – you have just expressed the Lutheran view extremely clearly and succinctly!

No-one is saying, “I heard the gospel preached; therefore I must be saved”. Rather, it is a case of saying: “I believe what Jesus said to me when he proclaimed the gospel to me through his minister; I believe what Jesus said to me when he said I am baptised”. And so on.

But the crucial thing – and I admit that Lutherans can sometimes fail to communicate this as clearly as we ought – is that it is the Holy Spirit’s work that enables us to believe what we are told in the gospel and sacraments. See my blog posts on this subject here and here (particularly the latter, which includes a crucial quote from the Augsburg Confession). If you don’t have the Holy Spirit within you, you won’t believe what you’re told in the gospel and sacraments; if you do believe what you’re told in the gospel and sacraments, then you can be sure the Holy Spirit is at work within you (because no-one can say “Jesus is Lord” without the Holy Spirit).

However, to make the question on which assurance hinges not “Do I believe these words that are proclaimed to me?” but “Do I have the Holy Spirit within me?” is to throw ourselves back on introspection and uncertainty. It also prompts me to ask the question: do you believe it is possible to believe the gospel, and yet not to have the Holy Spirit within you?

To put it another way: the Holy Spirit’s work is to make us believe what we are told in the gospel, not to make us believe that he is working within us. He points our attention outwards, towards Christ and the promises, not inwards to his work within us.