What does Malachi 3:11 mean?
Israel's covenant agreement with God included both positive and negative promises. If Israel complied, God had promised blessings. If Israel disobeyed, God vowed consequences (Deuteronomy 28:15–68). Verse 10 was an appeal for Israel to honor this agreement by bringing "the full tithe" to God's house. Prior verses, such as Malachi 3:8, explained that withholding part of God's required tithe was an act of robbery.In this case, it seems that the primary benefit promised is agricultural. Compared to modern farmers, ancient cultivators struggled greatly to combat insects and other natural threats to their crops. God's assurance that "the devourer" would not affect their crops is a promise of prosperity, so long as Israel honors their end of the agreement.
As with prior verses, it's important to remember that this two-sided covenant is between Israel and God, not between God and all Christian believers. In other words, this part of Malachi does not ensure material prosperity to believers who serve, donate to, or tithe on behalf of God. God certainly blesses those who are generous towards His church (Philippians 4:14–19), but this is not always a material return.