Micah 2:12-13 meaning

Following His word against the evil landowners and false prophets, the LORD then abruptly stated that He will surely assemble all of you, Jacob (v. 12). The phrase will surely assemble is literally "assembling I will assemble" in the Hebrew text. The repetition of the word "assemble" stresses the certainty that the LORD will again gather His people ("Jacob") someday. The inference is that "Jacob" will be exiled out of the land, but at some point will return again.

The second line in the verse is parallel to the first. The LORD says that He will surely gather the remnant of Israel. The phrase surely gather is also emphatic—"gathering I will gather." In this line, those whom the LORD will gather is called the remnant. These were Israelites (Jacob and Israel are synonyms) who remained faithful to the LORD and survived the LORD's judgment. 

Scripture indicates that God always preserves a remnant unto Himself (Romans 11:4-5). In this application, the remnant could also infer that many people will be killed or lost in their looming judgment, but the remainder of the nation would be gathered back to the land, as God promised in His covenant/treaty with His people (Deuteronomy 32:36, 43). 

The LORD describes His gathering of His remnant again in a more picturesque way. He declared that He will put them together like sheep in the fold. The LORD likens His people as sheep who would reside in the fold (Hebrew "bāṣrāh," "pen," "enclosure"), a place of protection and security. 

The LORD's people will also be Like a flock in the midst of its pasture. This demonstrates the LORD's role as Israel's provider. The pasture is a source of food and comfort. All of this will be given to them by their Shepherd-King (Psalm 23:1 - 4), even in exile (Isaiah 40:11; Jeremiah 23:3 - 4). Even though they will soon be devastated and exploited, God's plan for them is for them to prosper (Jeremiah 19:8-9, 29:11). 

The next phrase (They will be noisy with men) is probably best understood as painting a picture that when the LORD gathers His people (they) back into His pasture (the Promised Land), that there will be so many people it will sound like a noisy throng of sheep. This indicates that though Judah/Israel's population will be devastated, God will restore it, and make them numerous again.

When will this time of blessing happen? Note that the ten northern tribes had by this time been scattered by the Assyrians around 720 BC (2 Kings 17:5-6). And the two southern tribes were about to be exiled to Babylon, beginning around 605 BC. The Judeans were able to return from Babylon to the Promised Land around 535 BC, but Israel (the northern kingdom) did not return in antiquity. 

Later, Rome destroyed Jerusalem and dispersed the Jews throughout its empire in 70 AD. The Jews were scattered until the establishment of the nation of Israel in 1948 AD. However, this still does not fulfill all of this promised blessing. It is probable that the complete prophetic fulfillment Micah was describing is still in the future, at the time of this writing. Micah is likely describing what Israel's Shepherd-King will do in the Millennial Kingdom where Jesus will reign on this earth for a thousand years (Revelation 20:4-6).