Here is Ellen White on this question..
Author:
Ellen G. White Estate
A collection of Ellen G. White statements relating to the 144,000.
(See The Great Controversy, pp. 648,649 for basic statement)
A Non-Essential Question
"Christ says that there will be those in the church who will present fables and suppositions, when God has given grand, elevating, ennobling truth, which should ever be kept in the treasure-house of the mind. When men pick up this theory and that theory, when they are curious to know something it is not necessary for them to know, God is not leading them. It is not His plan that His people shall present something which they have to suppose, which is not taught in the Word. It is not His will that they shall get into controversy over questions which will not help them spiritually, such as who is to compose the hundred and forty-four thousand. Those who are the elect of God will in a short time know without question.
"My brethren and sisters, appreciate and study the truths God has given for you and your children. Spend not your time in seeking to know that which will be no spiritual help. 'What shall I do to inherit eternal life?' This is the all-important question, and it has been clearly answered. 'What is written in the law? How readest thou?" -Selected Messages, book 1, pp. 174, 175.
Strive to Be Among the 144,000
"Let us strive with all the power that God has given us to be among the hundred and forty-four thousand. And let us do all that we can to help others to gain heaven." -Review and Herald; March 9, 1905.
Mrs. White and the 144,000
"The Lord has given me a view of other worlds. Wings were given me, and an angel attended me from the city to a place that was bright and glorious. The grass of the place was living green, and the birds there warbled a sweet song. The inhabitants of the place were of all sizes; they were noble, majestic, and lovely. They bore the express image of Jesus, and their countenances beamed with holy joy, expressive of the freedom and happiness of the place. . . . I begged of my attending angel to let me remain in that place. I could not bear the thought of coming back to this dark world again. Then the angel said, 'You must go back, and if you are faithful, you, with the 144,000,* shall have the privilege of visiting all the worlds and viewing the handiwork of God."-Early Writings, pp. 39, 40.
Mrs. Hastings to Be With the 144,000
"I saw that she [Mrs. Hastings, who had just died] was sealed and would come up at the voice of God and stand upon the earth, and would be with the 144,000. I saw we need not mourn for her; she would rest in the time of trouble."-Letter 10, 1850 (2SM 263).
Silence is Eloquence
[The following letter from C. C. Crisler, leading secretary in Mrs. White's office, addressed to Elder E. E. Andross, president of the Pacific Union Conference, was called forth by a request from him to Sister White for any light she might have bearing on the teachings of Dr. B. E. Fullmer of Los Angeles, that the 144,000 will be made up of Americans only, none from other lands.]
"Elmshaven, Sanitarium, California, December 8, 1914. Dear Brother Andross: During the few minutes remaining of the noon hour before close of mails, after receiving your special delivery letter of inquiry, I sent you a hurried reply to your communication, promising further word by wire. Tonight I am sending [you] the following telegraphic letter:
"'Mrs. White instructs me to inform you she has no light further than that the presentation of uncertainties as certainties, and the urging of mysteries as revealed truths, is perilous and leads to disappointment. She suggests building on Holy Scriptures, the true foundation, rather than on personal conjecture.-C. C. Crisler.'
"When reading the letter to Sister White, and listening to her remarks in response, I had with me as a witness Elder D. E. Robinson.
"'I have no light on the subject,' she said, upon hearing the letter. 'It is a very delicate time in which we are living - a time when we must individually cling to the Lord with all the powers of our being.' She said further:
"Those who urge theories regarding matters that are not revealed, are placing themselves where they are in peril of meeting with disappointments. "Hide yourself in God; hide your mysteries in God"- these words have been repeated during the night season, over and over again. From the first, I have been instructed that the Lord Jesus can give counsel that will not bring disappointment.
"'Please tell my brethren that I have nothing presented before me regarding the circumstances concerning which they write, and I can set before them only that which has been presented to me.
"'There are those who attempt to deal with uncertainties as certainties; and when they reach this position, they are where it is possible for the enemy to use them.
"'In the past, light has been given me repeatedly that when a crisis arises, we are to take the counsel of God, and trace interestedly every item that presents the truth in its verity.
"'The greatest help will come when we see the influence of the teachings of the Holy Scriptures. Their influence is to lead us to stand on an exalted basis, where we will build our faith and the faith of others, not on this one's say-so, and that one's say-so, and another one's say-so, but on the real foundation, the Word of the living God.'
"I have tried to write out from my notes the words spoken by Sister White after listening to your letter and to portions of the letter written by me, also to my hastily written reply to you. By no word or sign did Sister White attempt to say which party is right and which party is wrong. In no wise did she make any comment on my letter you, and, so far as we could understand, in no wise did she attempt to interpret or explain that which she has written in former years regarding the 144,000. But, rising above mere detail, she outlined the principles set forth above.
"I have nothing to add to that which I wrote at noon. Yes, there is one comment Sister White did make when I was reading to her my letter. She expressed pleasure over the fact that I had included in my letter to you the words, 'On the matter of the exact meaning of the 144,000 Sister White has repeatedly instructed us that "silence is eloquence."'
"She also commented favorably upon hearing the words with which I closed, 'So far as I now know, no one knows the full truth of the matter, nor will we know until we are on the other side of Jordan.'
"I feel confident, Elder Andross, that the brethren in southern California will find blessing in reviewing the teachings of Scripture concerning the 144,000, and bringing to bear upon these teachings whatever light there may be in the published writings of Sister White. And as prayerful consideration is given the matter in all its bearings, I believe that God will make the truth sufficiently clear to make possible the avoidance of needless and unprofitable controversy over questions not vital to the salvation of precious souls.
"With kindest regards, and praying that God may give breadth of sympathy as well as clarity of vision to those called upon to handle this perplexing problem that has arisen, I am as ever, Yours truly, C. C. Crisler."
https://adventistbiblicalresearch.org/materials/theology-second-advent/counsel-regarding-question-144000Ellen G. White Estate December 21, 1964 Revised September, 1990
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*Note: Observe that the promise was given to Mrs. White that if she was faithful, she with the 144,000 would have certain privileges.