The Prime Minister said this was for the sake of the families and friends of the 298 people who perished in the tragedy.
"Malaysia wept for your loss, which was our loss too, and we will never let those who died be forgotten," he said in a post on his blog, NajibRazak.com.
"Take comfort in knowing that MH17 brought the country together in an act of unity that would make anyone proud to call themselves Malaysians. May that unity be the legacy of those we lost," he said.
Turning to the probe into the July 17, 2014, crash in troubled eastern Ukraine while the Malaysia Airlines plane was en route from Amsterdam to Kuala Lumpur, Najib said Malaysia would continue to provide full cooperation to - and work closely with - the Joint Investigation Team.
"They now have a clearer picture regarding the possible cause of the tragedy, and are expected to continue their investigation into all possible scenarios until the end of 2015," he said.
The prime minister said the end goal was clear - to bring the perpetrators to justice and ensure they paid for this crime which he described as unforgivable.
"The victims of MH17 were casualties of a conflict that was not theirs," he said.
He noted that by early October a report by the Dutch Safety Board on the MH17 tragedy would be published.
In the post, Najib recalled how Malaysia's decisive but consultative and unorthodox approach, including by engaging with rebels in the crash area, helped secure a safe passage and ensure the return of the remains of those aboard MH17.
In addition, he said, it also contributed in securing access to the wreckage and flight recorders that would help in getting to the truth on what happened on that fateful day.
"In those early days, we encountered criticism from various quarters, with segments of the foreign media calling on us to follow standard modus operandi.
"However, extraordinary circumstances require extraordinary measures, and we ignored those disruptive noises - standing our ground and doing it our way," he said.
On a more personal note, Najib said he remembered vividly the shock and anger he felt upon receiving that phone call on the MH17 crash.
He said the experience of leading the country through the tragedies of the MH370 crash in the southern Indian Ocean as well as MH17 in the space of mere months was still fresh in his mind.
"I hope that neither our nation, nor any other nation, has to endure such tragedies again," he said.