I see some echoes of pithy OT commentator Derek Kidner in R.T. France’s comments on the Sermon on the Mount. I thought this was an excellent set of comments on Matthew 7:7–8, “Ask and it shall be given…; seek and you will find…; knock and the door will be opened.”
The antidote to worry [6:25–34] is a robust confidence in God’s willingness to give his people all that they need. In vv. 25–34 the focus was explicitly on need rather than desire, and here too the son’s requests are for basic food, not for luxuries. It is therefore perhaps wise to read the unqualified offer of vv. 7–8 against that background: the “good things” which God will surely give do not necessarily include everything that his children might like to have. The “carte blanche” approach to petitionary prayer does not find support from the NT as a whole. It is God as the Father in heaven who knows what is “good” for his children, and as with a human parent his generosity may not always coincide with the child’s wishes. But for all that necessary caution, there is an openness about vv. 7–8 which invites not merely a resigned acceptance of what the Father gives, but a willingness to explore the extent of his generosity, secure in the knowledge that only what is “good” will be given, so that mistakes in prayer through human short-sightedness will not rebound on those praying.
R.T. France, The Gospel of Matthew, NICNT (Grand Rapids: Eerdmans, 2007), 279 (emphasis mine).