Tom Watson, Labour's deputy leader, has said his party has a "moral responsibility" to tackle antisemitism among its members.
He told guests at Labour Friends of Israel's annual lunch in Westminster on Tuesday he was ashamed of incidents of Jew-hate among Labour members.
"But dealing with it can't be something we do for show, for the sake of it, because we've come under media pressure, or because we need to deal with a political problem. It's a commandment," Mr Watson said.
"I know people here are understandably frustrated by how long it's taking the Labour Party to deal with antisemitism in our midst. You're right to be. It should have been quicker.
"I know there are still some outstanding issues that cannot be ignored. They won't be ignored. Action is being taken now and if, God forbid, we find these problems again, action will be quicker in the future."
Mr Watson attacked the anti-Israel boycott campaign, saying: "The BDS movement is morally wrong. It is failing."
He paid tribute to Shimon Peres, spoke of his friendship with Ian Austin, the Labour MP whose father escaped the Holocaust, and pledged his party's ongoing support for Israel.
Mr Watson appeared close to tears as he spoke of his trip to Israel last month, his work with the Holocaust Educational Trust and his friendships with Jews dating back to his time at Hull University, which, he said, had allowed him to "understand just what a remarkable story British Jews have to tell".
In a surprising opening to his address, the MP led diners in a rendition of the song Am Yisrael Chai (The People of Israel Live) before quoting the Talmud and Yehuda Bauer, the Shoah historian.
Mr Watson received a prolonged standing ovation from the 300 guests.
Joan Ryan, LFI chair, said while the past year had "not been the easiest for friends of Israel in the party", the group was "stronger and more determined".
She praised the Labour Students group for its efforts to tackle antisemitism. Ms Ryan also said Israeli and Palestinian youths should see each other as "potential team-mates" in their desire for peace.
Among the dozens of Labour MPs at the lunch were Shadow Chancellor John McDonnell, Dan Jarvis, Angela Eagle, Yvette Cooper and Chuka Umunna, who sat among communal leaders including Chief Rabbi Ephraim Mirvis.