As agrace said, you should study Malachi, Chapter 3 in its original context. God was dealing with and admonishing His people Israel through the words of the prophet Malachi within the theocratic and economic system He had set up for them. So many pastors preach Old Testament scriptures dealing only with the children of Israel as if they are promises made by God to, and literally applicable to, the church.
Yes, churches will build themselves. Pastors will work as cabbies on the side to make ends meet. Missionaries? Fuhgedaboutit.
Thanks so much for straightening me out on "context", sweetie. I feel refreshingly enlightened. I'll ignore lifelong teachings and many decades of personal experience and God's word, now that you have set me straight.