Logically, sacrificing Isaac would disallow this promise from being fulfilled. But Abraham also knew God was/is bigger than our logic; he knew that the things of God are, at times, counter-intuitive.
But seek first his kingdom and his righteousness, and all these things will be given to you as well.
-Matthew 6:33
Just as Isaac was of great importance to Abraham, so are multiple items in our own lives. Only a fool would not consider employment of importance, or having the finances to provide food for your family. God, too, understands the importance of these necessities. But God is also a jealous god.
If we ever find ourselves in the position of a consuming desire for any one of many "good" or "important" things, we may need to reevaluate our focus.
As the last half of Matthew 6 outlines (starting in verse 19) we can not serve two masters; we can not love God and money. This does not mean we are to discredit money completely. However, if it, or anything else, becomes a wearisome burden, weighing heavy upon your mind, it will usurp God from the throne of your heart and become a god itself. This is sin.
But do not lose sight of the hope given to us starting in verse 25 and climaxing in verse 33.
[D]o not worry about your life, what you will eat or drink; or about your body, what you will wear. Is not life more important than food, and the body more important than clothes?...So do not worry, saying, 'What shall we eat?' or 'What shall we drink?' or 'What shall we wear?' v. 25 & v. 31
But seek first GOD, and [then] all these things will be given to you as well. v. 33
