"Together, we will stand up to enemies like Iran bent on destroying Israel and her people," Trump said in the taped message, which lasted less than one minute and was shown at an event in Jerusalem.
The crowd of approximately 200 -- some wearing "Make America Great Again" caps -- cheered and chanted "Trump! Trump!" and "Lock her up!"
Republican vice presidential nominee Mike Pence also appeared in a pre-recorded video message, emphasizing the ties between America and Israel, and referring to Jerusalem as "the eternal, undivided capital of the Jewish people and the Jewish state."
"Israel is not just our strongest ally in the region. As I've said for so many years, Israel is our most cherished ally in the world," Pence said. "Donald Trump and I stand with Israel because Israel's fight is our fight. Israel's cause is our cause. And Israel's fate is our fate."
During the campaign, Trump has pledged to recognize Jerusalem as Israel's capital and move the American embassy from Tel Aviv to Jerusalem.
The Trump effort in Israel largely targeted two groups of voters: American-Israelis and evangelical Christians. With between 200,000 and 300,000 American voters living in Israel and the West Bank, Republican volunteers believe there may be enough votes to make a difference in some key swing states if the results are close.
David Friedman, Trump's policy advisor on Israel, spoke at the first gathering and accused the US State Department of being "anti-Israel and anti-Semitic for the past 70 years" because of its opposition to moving the US embassy to Jerusalem from Tel Aviv.
"When Donald Trump has his first meeting with the lifers in the State Department, they're going to say, 'Well, you know Mr. Trump, with all due respect, you've only been president for a couple of days, we've been living here for the last 20 years and we don't do it that way, we do it this way. We don't move the embassy,'" Friedman said.
"The reaction from Donald Trump will be, 'You know what guys, you're all fired,'" he added.
Trump has struggled to attract Jewish voters after critics have accused him of including and sharing anti-Semitic themes in his tweets and some of his followers have attacked Jewish journalists on Twitter. Trump has also had to disavow the support he has received from David Duke, the former head of the KKK, and the American Nazi Party.
Friedman also dismissed accusations of anti-Semitism among some Trump backers, saying, "There is far more anti-Semitism and anti-Israel sentiment among what I consider to be left-wing movements now than I think are on the right. Nobody thinks Donald Trump is anti-Semitic. No one thinks Donald Trump supports people that are anti-Semitic."