The Lord your God commands you this day to follow these decrees and laws

Deuteronomy 26:1-19

When you have entered the land the Lord your God is giving you as an inheritance and have taken possession of it and settled in it, take some of the firstfruits of all that you produce from the soil of the land the Lord your God is giving you and put them in a basket. Then go to the place the Lord your God will choose as a dwelling for his Name... Place the basket before the Lord your God and bow down before him. Then you and the Levites and the foreigners residing among you shall rejoice in all the good things the Lord your God has given to you and your household.

When you have finished setting aside a tenth of all your produce in the third year, the year of the tithe, you shall give it to the Levite, the foreigner, the fatherless and the widow, so that they may eat in your towns and be satisfied.

The Lord your God commands you this day to follow these decrees and laws; carefully observe them with all your heart and with all your soul. 

He has declared that he will set you in praise, fame and honor high above all the nations he has made and that you will be a people holy to the Lord your God, as he promised.

The first fruits and tithes; the summing up.

The instructions are for 'after you come into the land when the good things promised to come to fruition. The first fruits ceremony includes the recital of a lively prayer of remembrance and praise summarizing Israel's career.

Blessing comes through obedience. Israeli's is a high destiny, to bring God praise and fame and glory.

Why?

One more time God remind Israelites that the blessing is to obey God's command in the promised land. Such as devote the first fruit and the tithe. Take care of the fatherless and widows and the Levites.

Carefully observe God's commands with all your heart and with all your soul, for if do not care is easily fall into the astray of foreign custom and culture.

How?

Carefully observe them with all my heart and with all my soul.