John Gill Commentary Nehemiah 1:9

"but if ye return unto me, and keep my commandments and do them, though your outcasts were in the uttermost part of the heavens, yet will I gather them from thence, and will bring them unto the place that I have chosen, to cause my name to dwell there." — Nehemiah 1:9 (ASV)

But if you return to me, and keep my commandments, and do
them
Return by repentance, and, as a proof of the genuineness of it, yield obedience to the commands of God, and continue in it:

though there were of you cast out to the uttermost part of the
heaven ;
that is, the uttermost parts of the earth, the most distant regions; so called, because at the extreme parts of the horizon, according to our apprehension, the heavens and earth touch each other; so that what is the uttermost part of the one is supposed to be of the other:

yet will I gather them from there and will bring them to the place
that I have chosen to set my name there ;
that is to Jerusalem where the temple was built, and his name was called upon.