Abraham Receives the Promise Romans 4:18-20
…18In hope against hope he believed, so that he might become a father of many nations according to that which had been spoken, "SO SHALL YOUR DESCENDANTS BE." 19Without becoming weak in faith he contemplated his own body, now as good as dead since he was about a hundred years old, and the deadness of Sarah's womb;20yet, with respect to the promise of God, he did not waver in unbelief but grew strong in faith, giving glory to God,… http://biblehub.com/
What does this scripture tells us? 1) Be patient and consistent & 2) Rest in the will of God.
The nature and power of Abraham's faith are shown. Abraham believed God's testimony, and looked for the performance of his promise, firmly hoping when the case seemed hopeless. It is weakness of faith, that makes a man lie scrutinizing over the difficulties in the way of a promise. Abraham would not allow for an opportunity to present an argument or debate. Unbelief is at the bottom of all our staggerings at God's promises. Abraham's strength of faith was victorious over his fears. God honors faith and great faith honors God. Faith is a grace that of all others gives glory to God. Faith clearly is the instrument by which we receive the righteousness of God, the redemption which is by Christ.
When you feel as though your faith is weakening remember Abraham and remember Psalms 84:11, "For the LORD God is our sun and our shield. He gives us grace and glory. The LORD will withhold no good thing from those who do what is right."