Romans 4:18-21 meaning

When Abraham was given the promise from God that he would be the father of many nations, Abraham and Sarah were past childbearing age. There was no hope for Abraham to be a father with Sarah—according to all known human experience. But Abraham believed anyway. Why? Because God told Abraham that it would be: In 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" (v 18). 

The phrase so shall your descendants be is a quote from Genesis 15:5. God told Abraham that he would have an heir from his own body, then asked Abraham to step outside and look up at the stars. "This is how many descendants you will have," God promised Abraham. Although there was no way (humanly speaking) this could occur, Abraham believed, and God counted that belief as righteousness.

We have the opportunity to believe as Abraham believed. God asks us to believe that Jesus is God come to earth in a human body, who died that we may live, who promises us that His Spirit will come to live in us if we believe. It is impossible for us to validate this claim according to all we can see and experience prior to believing. But just as Abraham believed God anyway, so may we. God promises that if we believe, He will give us the gift of eternal life (John 3:14-16).

Abraham was not naïve; he reasoned that what God was promising was not possible according to all his experience: Without 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 (v 19). His body was as good as dead at least as it pertained to child rearing. Needless to say, if a 100-year-old man fathered a child, or a woman Sarah's age gave birth today, it would make headlines. Even at Abraham's time in history when long lifespans were apparently more common, 100 was still considered old.

Even though Abraham doubted the "reasonableness" of God's promise, his faith did not weaken. It is interesting to note that Abraham is not chided for reasoning. God made us with the faculty to reason, which is a part of being made in His image. But even though Abraham saw no possible way for God's promise to be fulfilled, he believed just the same.

Abraham understood that God is God, and God is not constrained by what we as humans consider reasonable. What we consider reasonable is based on our experience, and our experience is immensely limited, while God's is unlimited. This is the faith God elevates as an example for us to follow.

What Abraham did as he contemplated the human impossibility of God's promise to give him an heir in his old age, from his own body, was to grow even stronger in faith. Yet, with respect to the promise of God, he did not waver in unbelief but grew strong in faith, giving glory to God (v 20). The more Abraham reasoned, "This is impossible," the more he got excited to see what God would do. How is this so? Abraham gave glory to God.

What does it mean to give glory to God? In this case, it seems the next verse tells us the answer: Abraham was fully assured that what God had promised, He was able also to perform (v 21). This might seem confusing because of notions we have about what giving glory looks like. The Greek word "doxa" (translated glory) means for any object to have its true essence viewed by an observer. 1 Corinthians 15 tells us that the moon and sun have a glory, and their glory differs from that of terrestrial bodies like the earth (1 Corinthians 15:40-41). When any observer sees the sun for what it is, they are observing the sun's glory. The fact that the sun is not the earth takes nothing away from the sun, for it is not the earth. The earth has its own glory.

So God is glorified when He is made to be seen on earth as the personal Creator, the God that is the I Am, the Existent One. Psalm 19:1-2 says the heavens "declare" the glory of God, uttering speech and revealing knowledge about God. This is possible because the heavens reflect their Creator.

When Abraham believed God could do what seemed impossible, Abraham demonstrated for all to see that God is God, because God is dependable to do as He says. That is how Abraham gave glory to God.

God did not explain to Abraham how He intended to fulfill His promise of giving a son to Abraham from his own body, which was too old for children (v 19). It was yet fifteen or so years in the future when Abraham would see the promise fulfilled. Among many other promises, God tells us that He will cause all things to work together for good for those who love Him (Romans 8:28-29—in chapter eight of Romans, Paul will still be talking about believing the promises of God, and walking in the footsteps of Abraham, the father of those who believe).

God does not say we will understand how, at any point in time, bad can turn into something good. It often seems impossible for some things to ever come to any good. But in these times we have an opportunity to exercise the faith of Abraham because our Redeemer is faithful and true (Revelation 19:11). When we walk in faith, and abide in Christ, we bring Glory to God, because we are reflecting God to those who observe (John 15:8).