"What happens in the coming days will actually dictate what happens in the coming decades. We're running out of time. We're running out of possibilities," Kerry said in his address to the American Jewish Community Global Forum yesterday.
"Let's be clear: If we do not succeed now we may not get another chance. So we can't let the disappointments of the past hold the future prisoner.
"We can't let the absence of peace become a self-fulfilling prophesy. The absence of peace is perpetual conflict," he said.
"We will find ourselves in a negative spiral of responses and counter-responses that could literally slam the door on a two-state solution, having already agreed, I think, that there isn't a one-state one," Kerry said.
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"And the insidious campaign to de-legitimise Israel will only gain steam. Israel will be left to choose between being a Jewish state or a democratic state, but it will not be able to fulfill the founders' visions of being both at once," Kerry said.
"In this conflict, the simple fact is tomorrow is not guaranteed to look like today.
"And the people who think somehow because there is a fence and because there's been greater security and fewer people hurt are lulling themselves into a delusion that that somehow can be sustained. It cannot be," he said.
Kerry said the Palestinian Authority has committed itself to a policy of nonviolence.
"The fact that last year, up until recently, not one Israeli died from anything that happened from the West Bank until there was a settler killed about a month ago," he said.
"If the parties don't agree to come back to the table, the Palestinians have already said that they will go to the UN and seek to join more UN organisations, where, despite the best efforts of the United States, they will probably get more votes in their favour than they got last time.
"And last time, we only got nine votes against. And the Palestinians have also threatened to take their case to the International Criminal Court," Kerry warned.
"But wouldn't we both be stronger if we had some more company? With the right choices and enough courage and determination, there is a very different future possible for Israel," he argued.