Summary: The story of childless Abraham and Sarah and their miracle child Isaac is a story of faith in God, of trusting God against all odds, when the "natural mind" would say that the promised child (Isaac) was an impossibility. The vital message that comes through to us is: No matter what the obstacles, have faith in God!
Romans 4:16b-22 He is the father of us all....  Against all hope, Abraham in hope believed and so became the father of many nations, just as it had been said to him, “So shall your offspring be.”  Without weakening in his faith, he faced the fact that his body was as good as dead — since he was about a hundred years old — and that Sarah’s womb was also dead.  Yet he did not waver through unbelief regarding the promise of God, but was strengthened in his faith and gave glory to God,  being fully persuaded that God had power to do what he had promised.  This is why “it was credited to him as righteousness.”
King James Version, 20-21 He staggered not at the promise of God through unbelief; but was strong in faith, giving glory to God;  And being fully persuaded that, what he had promised, he was able also to perform.
•• By the way (vs. 22), this kind of unshakable faith is what prompted God to “credit it to him as righteousness” = saved!
• 20, KJV “He staggered not...” — against all odds, have faith in God!
•• Paul: “None of these things move me” (Acts 20:24).
•• 1 Corinthians 16:13...stand fast in the faith, quit you like men, be strong.
• 20 “...at the promise of God” —
•• The what? The “promise of God”! Why should we even think of staggering?!! How simple it ought to be to have faith in God when we consider the faithfulness of Him who promised!
•• 2 Corinthians 1:20 For all the promises of Godin him are yea, and in him Amen, unto the glory of God by us.
•• 1 Kings 8:56bNot one word has failed of all the good promises he gave through his servant Moses.
•• The desire to glorify God is perhaps a forgotten motive in our believing God for answered prayers and promises.
•• My friend, Pastor Tommy, made a hospital visit to a lady with a large goiter on her neck. Pastor Tommy simply laid hands on her and prayed, “Father, that you may be glorified, in the Name of Jesus, be healed!” And by the next morning the goiter was gone!
• 21 “...being fully persuaded” —
•• 2 Timothy 1:12, KJV ...I know whom I have believed, and am persuaded [NIV: convinced] that he is able to keep that which I have committed unto him against that day.
•• “fully persuaded” — James 1:6, KJV...let him ask in faith, nothing wavering.
• 21 “...He had promised” —
•• Titus 1:2 ...God, who does not lie, promised... It's not difficult to have faith in God's promises when we consider the utter impossibility of God lying to us.
• 21 “...He was able also to perform” —
•• Matthew 9:28 ...the blind men came to him, and he asked them, “Do you believe that I am able to do this?” “Yes, Lord,” they replied.
•• Luke 18:27 Jesus replied, “What is impossible with men is possible with God.”
Christ's disciples recognized the value of unshakable faith, so they properly appealed to Him, "Lord, increase our faith!" (Luke 17:5). As you seek God daily in prayer, in worship, and in His word, let that be your cry, too — "Lord, increase my faith!"
The apostle Paul lived out this message in his own life. During a furious storm on the sea, the Lord reassured Paul that they would be safe. Paul then encouraged his shipmates with the confident declaration: "So keep up your courage, men, for I have faith in God that it will happen just as he told me" (Acts 27:25). What better place to close this message than with Jesus' straightforward exhortation in Mark 11:22: “Have faith in God!"