For LDS, what does it mean that baptism is "essential" for "salvation"?

Question

https://abn.churchofjesuschrist.org/study/manual/gospel-topics/baptisms-for-the-dead?lang=eng

Jesus Christ taught that baptism is essential to the salvation of all who have lived on earth (see John 3:5). Many people, however, have died without being baptized. Others were baptized without proper authority. Because God is merciful, He has prepared a way for all people to receive the blessings of baptism. By performing proxy baptisms in behalf of those who have died, Church members offer these blessings to deceased ancestors. Individuals can then choose to accept or reject what has been done in their behalf.

At the same time, Mormon teaches in Moroni 8 that children who die before the age of accountability, don't need baptism, because they don't need repentance. And as far as I understand, being under a commandment requires knowledge of that commandment.

It's clear that, in order to be saved, even the dead have to accept Christ. But why do they need to subject themselves to a ritual that they can't themselves complete anymore?

In the phrase Jesus Christ taught that baptism is essential to the salvation of all who have lived on earth, what exactly is the meaning of "essential" and "salvation"?

Answer 1

There are conditional and unconditional antecedents to the remission of sins by the Savior.

Conditional:

To those who are accountable (revealed to be age 8 in D&C 68:27), repentance is required and once repented baptism is offered (baptism is for a remission of sins, sin requires knowledge of wrongdoing, children can't be held accountable, don't require baptism), and is a sign of the covenant they make with the Lord.

Unconditional:

For all those who are not responsible for their actions (those under 8, some with mental handicaps) the Lord has paid to the demands of justice the full price demanded for the sins that they have committed-unconditionally, fully, completely. The price has been paid, they are free and clean from the results or the effects of any wrong thing that they have done. They are not in a position to make and honor a covenant of obedience, so the covenant is not required of them, and the sign thereof therefore is not necessary. That great atoning sacrifice did not represent a postponement of justice, it satisfied justice!

Moroni 8:12-14

12 But little children are alive in Christ, even from the foundation of the world; if not so, God is a partial God, and also a changeable God, and a respecter to persons; for how many little children have died without baptism!

13 Wherefore, if little children could not be saved without baptism, these must have gone to an endless hell.

14 Behold I say unto you, that he that supposeth that little children need baptism is in the gall of bitterness and in the bonds of iniquity; for he hath neither faith, hope, nor charity; wherefore, should he be cut off while in the thought, he must go down to hell.

See Also:

• Do Babies need to be baptized
• If infants and little children pass from this life before being baptized, and if the only way to enter the celestial kingdom is through baptism, won’t they have to receive baptism at some future time?