While the hardness of the heart is a very standard metaphor, the contexts we have just seen make it particularly apt. We have seen metaphors of seeds, and seeds falling on hard ground would be a natural image here. We have more recently seen a reference to working metals, which might also have had a contextual allusion to hard and soft.
In any case, Amulek tells them to soften their hearts for the planting of the seed. He now speaks of the “time and the day.” The “time and the day” likely refer to an agricultural imagery of the time for planting. The “time” would perhaps be better rendered as “season” and the “day” of course is the time when planting occurs (as opposed to night). Of course what he means is that it should happen now. This immediacy of action is paralleled by the immediacy of the benefit. Amulek says that if they “immediately” (now is the time and the day) plant the seed of faith in the Christ, then “immediately” that atonement is applied to them.
How is it that the plan of redemption can be immediately applied? Isn’t there anything that they must do other than declare the name of Christ? Of course, but that is not the issue. Amulek is describing a relationship between a king and his people. The king possesses the right to dispense the benefit of the atonement, and he will do so for his people. Once they have become his people (by declaring his name – the same process Benjamin proposed in his speech) then they belong to the king, and are eligible for his benefits.
We should remember, however, that Amulek has already noted that once we are members of the community that we have communal obligations, and that failure to perform those obligations will remove us from that community of the people of the king. In the context of the imagery Amulek is using, he is precisely correct that by simply declaring the name they are immediately in a position to obtain the benefits.
The next verse simply reiterates the theme of immediacy. There is no other time when we might repent. Today is the time. The phrase “the day of this life is the day for men to perform their labors” likely refers to the daytime planting with which the farmers would be very familiar. Amulek has told them that it is “day” and that they must therefore “perform their labors.” That labor would be the planting of the seed. The imagery is complete. These farmers are being told to plant the seed of faith right now while the “time and the day” are right.