"People who say such things show that they are looking for a country of their own. If they had been thinking of the country they had left, they would have had opportunity to return. Instead, they were longing for a better country - a heavenly one. Therefore God is not ashamed to be called their God, for he has prepared a city for them." NIV translation
Those that are looking forward to the new heaven and the new earth, do not spend all of their time and energy on getting things in this world. When Abraham was called to leave his home and head to the promised land, he was not forced. He had a choice to make and he chose to believe that what was ahead was better than what was behind. We have that same choice to make when we are presented with the gospel of Jesus Christ. We can choose to accept it and shift our focus to the "promised land" or we can choose to reject it and stay with our old way of life.
"By faith Abraham, when God tested him, offered Isaac as a sacrifice. He who had embraced the promises was about to sacrifice his one and only son, even though God had said to him, 'It is through Isaac that your offspring will be reckoned.'" NIV translation
As we see here, God tested Abraham by asking him to sacrifice his only son. He did so even though it did not make sense to him.
Why would God test his faith (or ours)? The simple fact is that, at the end of the test, our faith will be stronger than before.
Imagine how strong his faith was after he saw God provide the sacrifice in Isaac's place.
"Abraham reasoned that God could even raise the dead, and so in a manner of speaking he did receive Isaac back from death." NIV translation
Abraham just thought that God would raise Issac from the dead even though he had never seen that done before. This reminds us that, as our faith grows, we will trust God to do things that we have never seen or even imagined.
"By faith Isaac blessed Jacob and Esau in regard to their future." NIV translation
Even while he was on his deathbed, Isaac held onto the promises of God and spoke of what He was going to do through Isaac's sons. This reminds us of the fact that sometimes we must just trust in God's promises knowing that we will not be around to see them fulfilled.