See Poole on "Matthew 9:37" and See Poole on "Matthew 9:38", where these words are put immediately before the sending out of the twelve. Both the twelve and the seventy, all that Christ ever sent out, were to be labourers in the Lord's harvest.
Related Commentaries of Luke 10:2
Luke 10:2
2 Therefore said he unto them,The harvest truly is great, but the labourers are few: pray ye therefore the Lord of the harvest, that he would send forth labourers into his harvest.