“let down.” The Greek word is ballō (#906 βάλλω), and it is usually translated “cast” or “throw,” but when the context warrants it, as a transitive verb it can also be used “of putting or placing someone or something somewhere: put (money into a treasury box), put (a sword into its scabbard), place (someone into a pool)” [Friberg’s Greek-English Lexicon]. In this context, the net is a dragnet, and they were placed in the water from a boat. Dragnets were placed parallel to the shore and then dragged by people to the shore, who gathered the fish, keeping the good and throwing the bad away. [For more information on fishing in Jesus’ time, see commentary on Mark 1:17].
“lake.” He was teaching from a boat on the Lake of Galilee, so the context dictates that thalassō be translated “lake.”
“and gathered fish of every kind.” The Kingdom of Heaven is the kingdom with heavenly qualities that is ruled by Christ when he comes from heaven, conquers the earth, and rules over it (Ps. 2:8; 72:8-11; Dan. 2:35; 7:14; Micah 5:4; Zech. 9:10). When Christ comes to earth and conquers it, there will be people of every sort left on earth, and the “good” will be allowed into the Kingdom, and the “evil” will be thrown away, into the Lake of Fire (Matt. 25:31-46; cp. commentary on Matt. 25:32).
[For more on the coming kingdom of Christ on earth, the Millennial Kingdom, see Appendix 3, “Christ’s Future Kingdom on Earth”].