1)
What is "Sichi"?
1.
Radak: It is my Tefilah.
2.
Malbim: It is pouring out the heart. Via signs and gestures, his weakness and affliction are recognized. This is impossible in the dark cave - but I can do so in front of Hashem!
2)
How will he be Magid his affliction?
1.
Radak: I will tell it in my Tefilah, even though He knows it 1 .
2.
Malbim: In the cave, there is no one to tell my external affliction, for there is no man to save me - but I will tell my affliction in front of Him!
1
Malbim (Metzora 79): Hagadah is telling all details, also matters that the listener did not know: He must explain here 'Agid' to be telling details that a human listener would not know. (PF)