Preaching vs. Bible Study

[frog]

As I've been reading my Bible more carefully and reading some of the reformed confessions and catechisms, preaching of the word stands out a lot!

In the Heidelberg Catechism:

65. Q. Since then faith alone makes us share in Christ and all His benefits, where does this faith come from?

A. From the Holy Spirit, who works it in our hearts by the preaching of the gospel, and strengthens it by the use of the sacraments.

And

83. Q. What are the keys of the kingdom of heaven?

A. The preaching of the holy gospel and church discipline. By these two the kingdom of heaven is opened to believers and closed to unbelievers.

In Westminster Standards:

Under the gospel, when Christ, the substance, was exhibited, the ordinances in which this covenant is dispensed are the preaching of the Word, and the administration of the sacraments of Baptism and the Lord’s Supper

And (WSC)

Quest. 89. How is the word made effectual to salvation?
Ans. 89. The Spirit of God maketh the reading, but especially the preaching of the word, an effectual means of convincing and converting sinners, and of building them up in holiness and comfort, through faith, unto salvation.

And when reading the Heidelblog it said:

The official proclamation of God’s Word is central to Paul’s understanding of how God has ordained to bring salvation to his elect. A Bible study, for all the value it has, however free God the Spirit is to operate through it, is not the preaching of God’s Word. The official, ordained, proclamation of the “word of Christ,” whether under the types and shadows looking forward—there is only one covenant of grace in multiple administrations—or in the New Covenant is the divinely ordained means of bringing to new life (regenerating) his elect.

And

The official preaching of the gospel is what the Reformed call “a means of grace.” For the benefits of a small-group Bible study on Sunday afternoon or evening, this divine promise is not attached to it.

That is an incredibly high view of preaching!

My question is in what way does preaching have promises attached to it that mean it's the ordained means over and above say a Bible study? Or really, any ministry that imparts information from the word; reading Bible, reading theology books, a teaching (but not preaching) series etc.?

In the past, whenever I read any of the passages of Scripture that talk about preaching and it being the activity people are saved through (Rom. 10), or foolishness, or pleasing God etc., I always took it to mean any speaking about the gospel. I've since come to appreciate that preaching means to "herald", quite a strong word. But I still think that really it's by the information from the Bible, whether read, in a Bible study etc., that God has promised to work through. He promised that His word won't return to Him empty (Isa. 55:11), it didn't then stipulate only if you preach it. He said the gospel is the power to save (Romans 1:16), so the good news is the channel through which they are saved. Not just the good news as long as you hear it preached on the street or in the church.

Having this theology, led to thinking such as; well then let's just get the good news (gospel) out in any way! Flyers, pamphlets, Bible studies, door-knocking, T-shirts, wristbands, you name it! We just need people to be imparted the information of the gospel, and that word which won't return empty (Isa. 55:11) and is what saves (Rom. 1:16) will save many, Lord willing!

What's wrong with my understanding?