Synagō (G4863) means to gather, collect, or assemble — people, crops, or things. It gives us the English word 'synagogue' (a gathering place). Jesus uses it to describe both the gathering of the blessed into the kingdom and the activity of the one who gathers with Him.
Matthew 12:30 sets up the ultimate binary: 'Whoever is not with me is against me, and whoever does not gather (synagōn) with me scatters.' The ministry of Christ and the church is a gathering ministry — calling the scattered sheep of Israel and the nations into one flock under one Shepherd (John 10:16). The eschatological harvest in Matthew 13 will be the final great gathering. Meanwhile the church 'gathering together' (synagomenoi) in Hebrews 10:25 is the foretaste.