What Jesus is saying is,
The great hindrance to having faith in God is pride, the pride that refuses to forgive.
That is like a mountain that fills up your whole life.
All you can see is that big mountain looming before you, and it is blocking the life of God in your life. You have the power to have that removed if, when you stand and pray, you will forgive those who have offended you.
Because the only thing that stops us from forgiving one another is pride. We feel justified in wanting others to forgive us but also in feeling that we have to exact a price for the hurt they have caused us. So, in many ways—subtle, or direct and open—we insist that we will not forgive, that our offenders have to pay for what they have done to us.
Somehow, we are going to make them crawl, make them beg or plead for forgiveness.
And that, Jesus says,
is a great mountain that needs to be removed, for it is blocking the flow of the life of God to your faith. So when you stand and pray, life will flow from God when you are able to recognize that you, too, need forgiveness.
Therefore I tell you, whatever you ask for in prayer, believe that you have received it, and it will be yours. And when you stand praying, if you hold anything against anyone, forgive him so that your Father in heaven may forgive you your sins.
God has forgiven you. God has offered it freely to you; give it just as freely to the one who has offended you.
After many years of ministry, I can recite evidence by the yard that this is true. The one thing above all else that seems to block the flow of the life of God to an individual, to a church, or to a nation, is this unwillingness to forgive, this holding of grudges, this desire to put somebody down in order to feel good yourself, this unwillingness to set these things aside and let God heal all the hurts of life.
That is why Jesus puts His finger on this one thing. Is this not amazing? The nation Israel lost its life because it would not forgive the Gentiles, the Romans, who had offended and grieved it. Instead, it gathered its robes of self-righteousness about it and looked with pride up to God and said,
I thank God I am not like these other people. God says that is what ends the life of a nation.
That is what ends the life of a church. And that is what ends the spiritual life of an individual, as it cuts him or her off.