"Everything is an affair of the spirit....."

"What if God does not want me to have what I need at this moment?"

If He does not want you to have something you value, it is to give you instead something He values.

"And if I do not want what He has to give me?"

If you are not willing that God should have His way with you, then, in the name of God, be miserable---until your misery drive you to the arms of the Father.

"Oh, but this is only about a mundane matter. I DO trust Him in spiritual matters."

Everything is an affair of the spirit. If God has a way of dealing with you in your life, it is the only way. Every little thing in which you would have your OWN way has a mission for your redemption. And He will treat you as a willful little child until you take your Father's way for your own.
-George MacDonald