From His Commentary on Song of Solomon II:14:
It is reported of the dove, that it will allure wild doves by its familiar converses into the dove-house with it: those who are called by grace, will use all proper ways and methods to allure and gain others to Christ, and to compliance with his ways and ordinances, as the church does the daughters of Jerusalem in this Song.
Do these sound like the words of someone who doesn't think that evangelism matters? Do they sound like the words of someone who opposes evangelism? It seems very clear to me that in this passage, Gill was advocating the proper "use of means for the propagation of the gospel to the heathen."