and being fully convinced that what He had promised He was also able to perform.
Romans 4:20-21 (NKJV)
Have you ever had someone tell you something that you did not think was really true? Maybe they told you about something that happened and you found it hard to believe that it could have happened as they said it did. But what if they had several friends with them who also said that this thing took place, would you believe it then? What if that person then showed you a picture or a video of what they were talking about, would you be convinced then? While you may not have believed what they said to start with and you had your doubts, eventually you were convinced that what was said was true.
When God promised that Abraham would have a son, Abraham was not convinced. In fact, he laughed and even tried to suggest to God how something else would work just as well. Abraham did not believe what God said but Romans 4 tells us that Abraham was fully convinced that God could do what He said. So how did Abraham go from not being convinced to being fully convinced? In Genesis 17 God changed Abram's name to Abraham. The name Abraham means, "father of a multitude", but this was not the natural reality in Abraham's life. Then in Romans 4:17 it quotes what is said in Genesis 17 and adds "God, who gives life to the dead and calls those things which do not exist as though they did".
Abraham made the decision to talk about himself in the same way that God did and that is the key. As Abraham continued to act and speak in faith, by simply saying what God had said, he grew stronger in his faith and became fully convinced that what God had said was true. Many people are weak in faith and unconvinced about what God says in His Word, first of all because they don't really know God's Word, and secondly because they are not talking like God talks or seeing themselves as God sees them. No matter what is happening in our life we need to go back to God's Word and see what God has to say about it and then speak and act accordingly.