"seek to gather souls from the corruption of the world into the saving purity of Christ's love. 7T 21.3"
"Let him know, that he which converteth the sinner from the error of his way shall save a soul from death, and shall hide a multitude of sins."
Both passages emphasize the importance of converting sinners and saving souls from death/corruption. EGW's statement directly echoes the sentiment and purpose described in James 5:20.
The formation of small companies as a basis of Christian effort has been presented to me by One who cannot err. If there is a large number in the church, let the members be formed into small companies, to work not only for the church members, but for unbelievers. If in one place there are only two or three who know the truth, let them form themselves into a band of workers. Let them keep their bond of union unbroken, pressing together in love and unity, encouraging one another to advance, each gaining courage and strength from the assistance of the others. Let them reveal Christlike forbearance and patience, speaking no hasty words, using the talent of speech to build one another up in the most holy faith. Let them labor in Christlike love for those outside the fold, forgetting self in their endeavor to help others. As they work and pray in Christ's name, their numbers will increase; for the Saviour says: “If two of you shall agree on earth as touching anything that they shall ask, it …
"Again I say unto you, That if two of you shall agree on earth as touching any thing that they shall ask, it shall be done for them of my Father which is in heaven."
Ellen White directly references Matthew 18:19 in this passage.
"For where two or three are gathered together in my name, there am I in the midst of them."
EGW directly quotes Matthew 18:20 after describing the formation of small groups, explicitly linking the two. The context of both passages is the power and presence of God within small gatherings of believers.