A lot of people don't get the good God has promised in the scripture simply because they don't follow the instructions linked to those benefits. In mathematics, there are often constrain to be fulfilled to solve particular problems. That is also how it is in the kingdom of God; if you want the blessings, you must first accomplish the conditions.
Isaiah 1:19 didn't just say “if you are willing”, it says it is necessary for you to also be obedient to eat the good of the land. The work of God says it is the Lord’s Supper, not the Lord’s Breakfast or Lunch. It is very straightforward; the Communion is to be done in the evening if you would get the good attached. Some other forks also say they haven't been getting the benefits of paying tithes as promised in the word of God.
The word of God says ALL, not some; it further says you are to bring the tithes to His storehouse. If you take it anywhere else or don't bring ALL, you shouldn't anticipate the benefits meant for faithful tithers. When you see a blessing in the word of God that you want to claim, look thoroughly for all the conditions that have to do with it. Fulfill the conditions and then you can have the benefit of the blessing.