"The just shall live by faith." (Hebrews 10:38) "But let him ask in faith, with no doubting, for he who doubts is like a wave of the sea driven and tossed by the wind. For let not that man suppose that he will receive anything from the Lord; he is a double minded man, unstable in all his ways". (James 1:6-7)
As Christian we live by faith. We receive all God's promises by faith and faith alone. Faith is knowing that you know that you know that you know, i.e. being convinced of Gods faithfulness. But at the same time if we speak words of doubt and unbelief, that shows we are double minded and we will not receive! Our words show what we are really believing. Watch what you say.