And it came to pass after these things, that God did tempt Abraham, and said unto him, Abraham: and he said, Behold, here I am. ² And he said, Take now thy son, thine only son Isaac, whom thou lovest, and get thee into the land of Moriah; and offer him there for a burnt offering upon one of the mountains which I will tell thee of.
³ And Abraham rose up early in the morning, and saddled his ass, and took two of his young men with him, and Isaac his son, and clave the wood for the burnt offering, and rose up, and went unto the place of which God had told him. ⁴ Then on the third day Abraham lifted up his eyes, and saw the place afar off. ⁵ And Abraham said unto his young men, Abide ye here with the ass; and I and the lad will go yonder and worship, and come again to you. Genesis 22:1-5 (KJV)

Here we have the account of God calling Abraham to sacrifice his one and only son, Issac. Now, the backstory on this is that Abraham and Sarah had received word from God that they would have a son. The only thing was that they were both quite old when they received this news. At first, neither of them believed God would do such a thing, they were like we are pretty old and even laughed at the idea. But their hearts changed and God was faithful as He promised.

Now, where we pick up here we see where God is testing Abraham and his faith. The word 'tempt' in verse 1 is not used in a negative sense, as one would be quick to think. In these usage, it means to test or prove. God has called on Abraham to sacrifice his only son, the same one He gave to Abraham and Sarah not long ago in their old age. But notice that even in the face of such a great request, Abraham trusts and acts in obedience and complete faith in God. 

Now we ask ourselves, would we have such a faith? And perhaps we ask, how did Abraham have such a great faith like this? 
The answer? Abraham choose to believe the promises of God that he had already been given to him by God.

And he brought him forth abroad, and said, Look now toward heaven, and tell the stars, if thou be able to number them: and he said unto him, So shall thy seed be. And he believed in the LORD; and he counted it to him for righteousness. Genesis 15:5-6

In Genesis 21:12, And God said unto Abraham, Let it not be grievous in thy sight because of the lad, and because of thy bondwoman; in all that Sarah hath said unto thee, hearken unto her voice; for in Isaac shall thy seed be called.
With those promises, Abraham's choice to trust God as he led Issac up that mountain to sacrifice meant that either he trusted that God would spare Issac or, if he did die, that God would bring him back to life, based on the earlier promise God had given him.
So, here is our question. What is God calling YOU to do? And, what promises do you have that can enable you to trust that God is in control and will provide? Even when what God asks us to do might seem, shall we say, radical. But we are called to have a radical faith in God, to trust Him for what we can not do or even understand.