Galatians 3:6

6 Thus Abraham believed in and adhered to and trusted in and relied on God, and it was reckoned and placed to his account and credited as righteousness (as conformity to the divine will in purpose, thought, and action).

Now ask yourself this question, did Abraham believe what God had for him on his own? Did Abraham adhere to and rely on our Father through his own human strength and ability to believe? No. Abraham was told by the Lord, as he ate with Him, that he was going to have a son, Genesis 18. Go and read Genesis 18, you will see that Abraham actually ate with the Lord. The Lord came down to Abraham and ate with Him! Then the Lord told Abraham what He was going to do with Sodom and Gomorra. Abraham was not left on his own to believe God. 

Our Father has always been the power that worked within men to inspire faith. The Truth is that the Holy Spirit worked through men even before the Cross.

The Lord said to Moses, Take Joshua son of Nun, a man in whom is the Spirit, and lay your hand upon him; Numbers 27:18

And Moses said to the Israelites, See, the Lord called by name Bezalel son of Uri, the son of Hur, of the tribe of Judah; And He has filled him with the Spirit of God, with ability and wisdom, with intelligence and understanding, and with knowledge and all craftsmanship, Exodus 35:30-31

The Spirit of the Lord came upon him, and he judged Israel. He went out to war, and the Lord delivered Chushan-rishathaim king of Mesopotamia into his hand and his hand prevailed over Chushan-rishathaim. Judges 3:10

For he (John the Baptist) will be great and distinguished in the sight of the Lord. And he must drink no wine nor strong drink, and he will be filled with and controlled by the Holy Spirit even in and from his mother's womb. Luke 1:15

Our Father was active in people’s lives even before Jesus came and died for us. We have to remember the Truth, nothing exists that isn’t controlled by our Father. Whether things are seen or unseen, whether they are in Heaven or on earth, everything is controlled and has always been controlled by our Father.

All things were made and came into existence through Him; and without Him was not even one thing made that has come into being. John 1:3

For it was in Him that all things were created, in heaven and on earth, things seen and things unseen, whether thrones, dominions, rulers, or authorities; all things were created and exist through Him [by His service, intervention] and in and for Him. And He Himself existed before all things, and in Him all things consist (cohere, are held together). Colossians 1:16-17

The Truth is that our Father has always been with us and He has always controlled everything. It just has to be that way, because nothing can exist without Him. So Abraham was not left on his own to believe our Father, just as we are not left alone to believe Him. Faith for us has always come from our Father and it always will. Even Jesus prayed in John 17 for our Father to glorify Him, so that He could in turn glorify God. The flesh of God required the Spirit of God to empower Him. If there was any flesh that could have done it on His Own it would have been Jesus, but even Jesus couldn’t. For flesh to have faith and serve the Kingdom it all has to come from the Holy Spirit, flesh on its own just doesn’t have the ability.