1.  Presenting The First Fruit  (Deut 26:1-11) 
2.  Presenting The Tithe  (Deut 26:12-15)

These commandments were a special declaration of thanksgiving to YHVH for the land and were specifically chosen to conclude this section of the main speech. 

First Fruit:  "You shall then recite: YHVH brought us to this place and gave us this land, a land flowing with milk and honey, therefore I now bring my first fruits of the soil which You have given me."  (Deut 26:9-10) 

The Tithe:  "When you set aside your tithe... you shall declare before YHVH: I have fulfilled all of my obligations. Look down from heaven and bless Your people Israel and the soil You have given us, a land flowing with milk and honey, as you swore to our fathers."  (Deut 26:12-15)

Both times we thank YHVH for the Land and recall His covenant with the Fathers.

In the commandment of first fruit we don't thank YHVH for  the fruit, rather, we 'use' our first fruit in order to thank YHVH for the land.

Each of these declarations relate to YHVH's covenant with the Fathers concerning the Promised Land.  Recalling the covenant, we thank YHVH for fulfilling His promise to our forefathers and remind ourselves of the reason why he gave us the land - to become a holy nation and glorify Him.  (Deut 4:5-8)