It said "Hashem b'Kirbech" (15). Why is this repeated?
Radak: Since He is amidst you, do not slacken (refer to 3:17:2:1).
What do we learn from "Gibor Yoshi'a"?
Rashi: Hashem is a Gibor - He will save from [Radak - the Giborim of] the Nochrim.
Malbim: Do not fear that Hashem, who saves, is not amidst you - He is amidst you! Do not fear that He cannot save - He is Gibor!
What do we learn from "Yasis Alayich b'Simchah"?
Malbim: Do not fear that He will not want to save, or that He will abandon you - just the contrary, He will be Mesis over you! Masos is external signs to show Simchah. "B'Simchah" teaches that He will rejoice with Simchah of the heart, like one who marries a [new] wife, and unlike one who remarries his divorcee. The latter does external signs of Simchah, but his heart does not rejoice.
Why will He be silent amidst His love?
Rashi, Targum Yonasan: He will cover (Radak - be silent about) your sins amidst His love for you.
Malbim: He will think deeply 1 how to add to you spiritual goods constantly.
All of these are mere anthropomorphisms. Hashem always knew everything. Deep thinking cannot add to His knowledge! (PF)
Why does it add "Yagil"?
Malbim: Gil is Simchah over something new, like a found object or good tidings. In addition to the constant Simchah that He will have over you, He will constantly do for you new signs and wonders, and you will constantly rise in the level of perfection.