# General Information:

Moses continues to speak to the people of Israel. He speaks as though they were one man, so all instances of "you" and "your" are singular. 

# But from there

"But when you are in those other nations"

# you will seek

The word "you" here is plural. 

# when you search after him

"when you really try to find him" or "when you really try to know him"

# with all your heart and with all your soul

"completely" or "earnestly."