We were just reading Hebrews 3 where it says that the Lord has sworn in His wrath that those who sinned in the wilderness – and were made to wander forty years – will not enter into His rest. Does this mean they cannot obtain the Celestial Kingdom?
While researching the answer to your question, I realized you are quoting Hebrews 3:8:
8 Harden not your hearts, as in the provocation, in the day of temptation in the wilderness:
Here, the Lord was referring to the children of Israel after they were delivered from slavery by Pharaoh and wandered in the wilderness for 40 years (as it turns out, sinning), which we can read in Numbers 14:2–23:
2 And all the children of Israel murmured against Moses and against Aaron: and the whole congregation said unto them, Would God that we had died in the land of Egypt! or would God we had died in this wilderness!
3 And wherefore hath the Lord brought us unto this land, to fall by the sword, that our wives and our children should be a prey? were it not better for us to return into Egypt?
4 And they said one to another, Let us make a captain, and let us return into Egypt.
5 Then Moses and Aaron fell on their faces before all the assembly of the congregation of the children of Israel.
6 ¶ And Joshua the son of Nun, and Caleb the son of Jephunneh, which were of them that searched the land, rent their clothes:
7 And they spake unto all the company of the children of Israel, saying, The land, which we passed through to search it, is an exceeding good land.
8 If the Lord delight in us, then he will bring us into this land, and give it us; a land which floweth with milk and honey.
9 Only rebel not ye against the Lord, neither fear ye the people of the land; for they are bread for us: their defence is departed from them, and the Lord is with us: fear them not.
10 But all the congregation bade stone them with stones. And the glory of the Lord appeared in the tabernacle of the congregation before all the children of Israel.
11 ¶ And the Lord said unto Moses, How long will this people provoke me? and how long will it be ere they believe me, for all the signs which I have shewed among them?
12 I will smite them with the pestilence, and disinherit them, and will make of thee a greater nation and mightier than they.
13 ¶ And Moses said unto the Lord, Then the Egyptians shall hear it, (for thou broughtest up this people in thy might from among them;)
14 And they will tell it to the inhabitants of this land: for they have heard that thou Lord art among this people, that thou Lord art seen face to face, and that thy cloud standeth over them, and that thou goest before them, by day time in a pillar of a cloud, and in a pillar of fire by night.
15 ¶ Now if thou shalt kill all this people as one man, then the nations which have heard the fame of thee will speak, saying,
16 Because the Lord was not able to bring this people into the land which he sware unto them, therefore he hath slain them in the wilderness.
17 And now, I beseech thee, let the power of my Lord be great, according as thou hast spoken, saying,
18 The Lord is longsuffering, and of great mercy, forgiving iniquity and transgression, and by no means clearing the guilty, visiting the iniquity of the fathers upon the children unto the third and fourth generation.
19 Pardon, I beseech thee, the iniquity of this people according unto the greatness of thy mercy, and as thou hast forgiven this people, from Egypt even until now.
20 And the Lord said, I have pardoned according to thy word:
21 But as truly as I live, all the earth shall be filled with the glory of the Lord.
22 Because all those men which have seen my glory, and my miracles, which I did in Egypt and in the wilderness, and have tempted me now these ten times, and have not hearkened to my voice;
23 Surely they shall not see the land which I sware unto their fathers, neither shall any of them that provoked me see it:
In the teacher’s institute manual we read:
As “the Apostle and High Priest of our profession,” Jesus Christ is greater than the prophet Moses. Paul encouraged the Hebrew Saints to remain faithful and not to harden their hearts as ancient Israel did in the wilderness. This provoked the Lord to anger and prevented the ancient Israelites from entering into His rest, which the Lord defined as the “fulness of his glory” (D&C 84:24). (emphasis added)
If you continue and study the scriptural reference given in the last quote, we read:
24 But they hardened their hearts and could not endure his presence; therefore, the Lord in his wrath, for his anger was kindled against them, swore that they should not enter into his rest while in the wilderness, which rest is the fulness of his glory. (emphasis added)
Why was there a mention of: “they should not enter into his rest while in the wilderness“?
I would love to think that the atonement is powerful enough to cover a multitude of sins, among other things. Although, sin does keep us from the presence of God, and prevents us from “enjoying the fulness of His glory”, through genuine and honest repentance, we can always come back into His presence.
This is a great reminder of the power of repentance and forgiveness, AND, the power of following the counsel of our leaders to obey, follow and keep the commandments. So, will they obtain Celestial kingdom? It is up to the Lord to decide and judge if they are worthy; but I would venture to say that if they repented and are baptized and are humble to follow him and accept him as their savior, then I have no doubt that the chances of gaining a celestial glory are very high.
I hope this answered your question.