Physical mindset can change gradually.
For instance,
It will happen, may be it will happen, i dont have any hope about it and finally its never gonna happen.
So depending upon the times, our mindset may change.
But faith is totally different from that.
It's an assurance. But for that believing physically not enough.
It is spiritually connected.
Israelities by there own eyes had seen all wonders done by God in the wilderness, but they raged against God every time when something was needed. So physically they had understood power of God. But they forgot after sometimes.
I don't want u to make believe everything bible tells blindly, but test in a good way.
In the days of old testament, Spirit of God was upon particular peoples who was leading.
So they had the assurance of God is working for present as well as future. Because Holy Spirit testified all the things to them.
But now, Holy Spirit of God has given through Jesus Christ to everyone who believes in His name. So if we receive Holy Spirit, he will give that assured faith(1cori 12:9).
So u will ask which Holy Spirit.
But only one Holy Spirit is here, that is Sprit of God.1(cori 12:4).