The Old Testament and the New differ like chess and rugby, but God does not change

Similarly watching God deal with Israel in their marriage covenant with Him teaches us a lot about about how He will deal with us in our marriage covenant. Just like Chess and Rugby's rules and requirements differ, so the Mosaic and the New Covenant differs.

But He is the same God ...

Point 1 Moses law was a marriage covenant between God and Israel

Point 2 The New Covenant is a marriage covenant between God and the Church.

Point 3 God is the same but the covenant is not.

Telling the little ones about David and Goliath is useful and powerful

Yanking Malachi 3:10 out of its context into the new covenant is like arbitrarily applying one chess rule to the rugby game while ignoring the other 613 rules.

If you don't know chess rules and rugby rules the games will both be useless and boring to watch. Also even though your might have been a gifted rugby player you will now never be able to play and excel if your education has been an arbitrary hotch-potch of chess rugby rules.

You will also never really understand who God is.