1)
Why did he say "Re'eh Atah"?
1.
Malbim: See that Hashem did wondrous good with you.
2)
What is the significance of "Hashem Bachar Becha Livnos Bayis l'Mikdash"?
1.
'Rashi': You will not build it for Him to live in it - Shamayim cannot contain Him! Rather, it is for a Mikdash - for the sake of the Aron, which is called Mikdash - "v'Nas'u ha'Kehasim Nose'ei ha'Mikdash", i.e. the Aron. He did not pick you because you are more praiseworthy than others, rather, for His sake, and due to His mercy.
3)
Why did he conclude "Chazak va'Ase"?
1.
Malbim: First one must build the Mikdash Hashem in his heart, until Hashem dwells in his Ru'ach and Nefesh. Only after, he can build the Beis ha'Mikdash.
