The terror group was guilty of "unimaginable horror," Merkel told MPs in her statement. "They cruelly clear everything away which doesn't fit their world view. Here a religion is misused in a terrible way, to justify murder, terror and the rule of violence."
"The immense suffering of many people cries to the heavens," the Chancellor said, "and our security interests are threatened."
400 German citizens were currently fighting with Isis in Iraq and Syria and could return to carry out attacks in Europe, she added.
"We now have a chance to stop the terrorists from creating a new safe haven. We have to take this chance."
The choice had nevertheless been "weighed up with great care," Merkel emphasized.
Merkel stressed that weapons deliveries would only be the beginning, saying that "as we in Europe have learned, conflicts are only solved in the long term politically." She outlined a number of measures that must be taken to improve governance in Iraq including improved protection of human rights and more freedom for the autonomous Kurdish-controlled region.
For the first time, weapons from the Bundeswehr (German army) arsenal will be sent, including 40 machine guns, 500 anti-tank rockets, 16,000 rifles and 10,000 hand grenades.
Defence Minister Ursula von der Leyen said on Sunday that the arms would be used to outfit 4,000 Kurdish soldiers by the end of September. Some of the soldiers may be brought to Germany to be trained in their use.
“The situation in Iraq is extremely critical,” she said, accusing Isis of “merciless brutality”.
In a symbolic vote late on Monday, the Bundestag supported the government's plans, with CDU/CSU and SPD members voting for and the Left and Green parties largely opposed.
Left party leader in the Bundestag Gregor Gysi and Green leader Anton Hofreiter said that Germany would lose control of the weapons once they had been delivered.
"No-one can control where these weapons will end up or to what purpose they will be put," Hofreiter told parliament.
Both sides of the Christian-Democratic (CDU) and Social-Democratic (SDP) coalition had already agreed on the plan before the vote.
Foreign Minister Frank-Walter Steinmeier said on Sunday that “[Germany's] help for Iraq and our measures against Isis don't begin with weapons shipments and don't end with weapons shipments.”
However, Steinmeier shared his concerns about arming the Kurds, possibly enabling their longer-term goal of an independent state, in an interview with the Hannoverschen Allgemeinen Zeitung.
"An independent Kurdistan in northern Iraq would lead to more secessions in the rest of the country," he said, causing "new battles over new borders and state territories."
But Merkel in her statement said that "What is, is more important than what could be," in her decision to send weapons to the Kurds.
Political rhetoric has been building up to a change in German policy in recent days, with Merkel outlining the risk of “genocide” committed by Isis in remarks last week.
People interviewed by The Local on Berlin's Alexanderplatz yesterday had mixed views about Germany's decision to intervene in the conflict:
SEE ALSO: Merkel accuses Isis of 'genocide'