ordained = made, or appointed. In the sense of Hebrew. dsah, in 1Sa_12:6 ("advanced").
that = in order that.
be with Him. This is the first great qualification for any thus called and sent. (1) Like Abel, to have "peace with God"; then (2) like Enoch, to walk with God", and (3) like Noah, to witness for God (Heb_11:4-7).
might = should.
send them forth = Greek. apostello. This is the second great qualification here. For the others, see above and Act_1:22.