The Lord will open to you his good treasure in the sky, to give the rain of your land in its season, and to bless all the work of your hand: and you shall lend to many nations, and you shall not borrow. — Deuteronomy 28:12
Again, the Kingdom of Heaven is like a treasure hidden in the field, which a man found, and hid. In his joy, he goes and sells all that he has, and buys that field. — Matthew 13:44

Author
Charles Spurgeon
Summary: The Lord promises to send rain in its season, a picture of the heavenly refreshment with which he renews his people. His good treasure is not reserved for great prophets: every believer can come to him and pray for their brothers and sisters too. We can ask with confidence if we remain in Christ and his words remain in us. We do not yet know all his treasures or fully enjoy the riches of the covenant. Only the Lord can open our understanding, direct our hearts toward his love, and reveal Jesus in us. Let us listen attentively to his voice and obey his will.
This refers first to rain. The Lord will give it in its season. Rain is the emblem of all those heavenly refreshings that the Lord is ready to bestow on His people. Oh, may we have a plentiful rain to refresh the Lord’s inheritance!
It seems that we think God’s treasury can be opened only by a great prophet like Elijah, but that is not so, for this promise is for all the faithful of Israel and, indeed, for every one of them. Oh, believing friend, “The Lord will open to you His good treasure.” You too can see heaven opened, reach in and take your portion—yes, and a portion for all your brothers and sisters around you. Ask for whatever you wish, and it will not be denied you, if you abide in Christ and His words abide in you.
You have not yet known all the treasures of your Lord, but He will open them to your understanding. Certainly you have not yet enjoyed the fullness of the riches of the covenant, but He will direct your heart toward His love and reveal Jesus in you. Only the Lord Himself can do this for you; but here is His promise, and if you listen diligently to His voice and obey His will, His riches will be yours in glory through Christ Jesus.
Source: The Checkbook of the Bank of Faith. Translation by Allan Roman.
http://www.spurgeon.com.mx/chequera/meditames/mayo.pdf