So I ask again, why does Ps. 127:3 have a regulative import on the NT church, but the references in Ezekiel and Joel do not, which indicate they are God's children and a part of God's congregation?
Matthew - in reading Ezekiel 16 in context, I still don't see a disconnect. God (through the prophet) is telling Israel that she came from near death and was blessed and established by God. This chapter shares similar themes with that of the Song of Solomon. You can almost see chapter 3 of Ruth when God says, Ezekiel 16:8 8 "Then I passed by you and saw you, and behold, you were at the time for love; so I spread My skirt over you and covered your nakedness. I also swore to you and entered into a covenant with you so that you became Mine," declares the Lord God. But keeping Romans 9:6 in mind, this covenant does not mean all of Israel were of faith. In fact, the Lord alludes to this in verses 15-24 when he details Israel's adulteries.
When the Lord indicts Israel (vs. 20-21), He calls their children "Mine." Is the Lord saying these chidren are saved? Is their part in the covenant equal with being regenerate? No. These children belonged to God just as Israel belonged to God (vs. 8).
Joel 2 is similar to Ezekiel in that the nation had played the harlot and was facing judgment. The very fact that Israel had turned her heart to other God's and abandoned the LORD their God is proof that not all were of faith. Did God have a covenant with Israel? Of course! Did Israel play the harlot, and Judah too? Again, of course! But did not Moses warn the nation of God's severe wrath for forsaking the LORD God (Deut. 28)? Because the nation was under covenant, the nation was called to repent. In Joel 2:16 the situation Israel faced was so desperate that all were called to repent. Indeed, in verse 3 the LORD tells the people, ...rend your heart and not your garments." What was the LORD looking for? He was looking for the same Israel that Paul was describing in Romans 9.
Matthew, I am sure you will disagree with my exegesis, but please do not say that I have avoided the passages you asked about.