This phrase is used here to mark the beginning of a new part of the story. If your language has a way for doing this, you could consider using it here.
Walking is a metaphor for living, and "before me" or "in my presence" here is a metaphor for obedience. AT: "Live the way I want you to" or "Obey me" (See: [[rc://en/ta/man/translate/figs-metaphor]])
Here "multiply you" is an idiom that means he will give him more descendants. AT: "greatly increase the number of your descendants" or "give you very many descendants" (See: [[rc://en/ta/man/translate/figs-idiom]])