Alma 42:24-27

24  For behold, justice exerciseth all his demands, and also mercy claimeth all which is her own; and thus, none but the truly penitent are saved.
25  What, do ye suppose that mercy can rob justice?  I say unto you, Nay; not one whit.  If so, God would cease to be God.
26  And thus God bringeth about his great and eternal purposes, which were prepared from the foundation of the world.  And thus cometh about the salvation and the redemption of men, and also their destruction and misery.

Alma 42:24-26 (Emphasis mine)

Alma 42:22-23 teaches us that, through the atonement of God, and through repentance, mercy can meet the demands of justice and we may be redeemed.

Alma(2) continues by telling us that while "mercy claimeth all which is her own" only the "truly penitent are saved.  Merely repenting is not enough.  We must be "truly penitent." (emphasis mine).  That does not mean that "mercy can rob justice ... Nay; not one whit."  The demands of justice must be met.  But they are met by God's "great and eternal purposes, which were prepared from the foundation of the world."  From the beginning, God prepared a way for man to obtain "salvation and the redemption of men..."  This was the way God prepared so that "mercy claimeth the penitent, and mercy cometh because of the atonement."  (v23) (Emphasis mine).

Peter wrote:

2  Grace and peace be multiplied unto you through the knowledge of God, and of Jesus our Lord,
3  According as his divine power hath given unto us all things that pertain unto life and godliness, through the knowledge of him that hath called us to glory and virtue:
4  Whereby are given unto us exceeding great and precious promises: that by these ye might be partakers of the divine nature, having escaped the corruption that is in the world through lust.

2 Peter 1:2 - 4 (Emphasis mine)

We live in a corrupt world.  Sin is an every day part of our world,  Peter tells us that through the atonement, we are able to "[escape] the corruption that is in the world..." (v4) by and through the teachings of Christ that "pertain unto life and godliness..." (v3).

27  Therefore, O my son, whosoever will come may come and partake of the waters of life freely; and whosoever will not come the same is not compelled to come; but in the last day it shall be restored unto him according to his deeds.

Alma 42:27 (Emphasis mine)

Alma(2) tells Corianton that we have a choice.  We can "partake of the living waters of life freely" or we can choose to not partake.  Whichever choice we make will be "restored unto [us] according to [our] deeds."  Whether we are saved and return to the presence of God because we accept the mercy God offers us through the atonement or whether we remain in our spiritual fallen state and face justice and become  eternally cut off from God is our choice.  God will not force us.  We can either partake of mercy  or face justice.  It's our choice.