I confess to having promised someone "I will pray for you" and then not praying for them. There is something false about that. It is not right to make a promise and then not come through on it. That is disingenuous, and has the character of a lie.
"Promising to pray" is not the same as "praying." What we need are people who actually pray, not people who promise to pray but never actually praying. James 5:16 says "the prayer of a righteous person is powerful and effective." Promising without praying, I assume, lacks such power and effectiveness. Here we are told that prayer effects results. Merely promising someone that you will pray for them effects nothing in God's Kingdom. Perhaps in that other, dark kingdom there is a celebration over another Jesus-follower who chose not to make good on their promise?
Why would someone make a promise and not keep it? A father promises his son "I'll take you fishing this summer" but it never happens. Another says "I will call you," but the call never comes. It seems that many stated promises are left unkept. The unkept promise momentarily flatters, and later breeds bitterness. It becomes a way of putting someone off. Unkept promises feel ike rejections. How easy it is to say you will do something and never do it. The heart of this is: you, not the other person.
"Promising" is covenant behavior. In a promise we attach ourselves to someone. The unkept promise reveals the lie of false attachment.
I love our church's e-prayer team. I know I have, in them, a people who don't just say they will pray, they do pray. I see this in results. I attribute much of the good God-things now happening at Redeemer to the prayers of our people. They said they would pray. They have. We are a praying church.
