# For if you diligently keep all these commandments that I am commanding you, so as to do them

"For if you are careful to do everything that I have commanded you"

# walk in all his ways

A person obeying Yahweh is spoken of as if he were walking on Yahweh's ways or roads. 

# to cling to him

"to rely on him" or "to have a good relationship with him". See Deuteronomy 10:20.