What is the meaning of Luke 8:13?

They on the rock [are they], which, when they hear, receive the word with joy; and these have no root, which for a while believe, and in time of temptation fall away. (Luke 8:13 KJV)

And those on the rock [are] they who, when they have heard, receive the word with joy; and these have no root, who for a while believe, and in time of temptation fall away. (Luke 8:13 ASV)

But those upon the rock, those who when they hear receive the word with joy; and these have no root, who believe for a time, and in time of trial fall away. (Luke 8:13 DBY)

Those on the rock are they who, when they hear, receive the word with joy; but these have no root, who believe for a while, then fall away in time of temptation. (Luke 8:13 WEB)

And those upon the rock: They who, when they may hear, with joy do receive the word, and these have no root, who for a time believe, and in time of temptation fall away. (Luke 8:13 YLT)

Interlinear

<de> They on <epi> the rock <petra> are they, which, <hos> when <hotan> they hear, <akouo> receive <dechomai> the word <logos> with <meta> joy; <chara> and <kai> these <houtos> have <echo> no <ou> root, <rhiza> which <hos> for <pros> a while <kairos> believe, <pisteuo> and <kai> in <en> time <kairos> of temptation <peirasmos> fall away. <aphistemi> (Luke 8:13 KJV)

 Robertson’s NT Word Pictures

Which for a while believe (hoi pros kairon pisteuousin). Ostensibly they are sincere and have made a real start in the life of faith. They fall away (aphistantai). Present middle indicative. They stand off, lose interest, stop coming to church, drop out of sight. It is positively amazing the number of new church members who “stumble” as Mr 4:17 has it (skandalizontai), do not like the pastor, take offence at something said or done by somebody, object to the appeals for money, feel slighted. The “season of trial” becomes a “season of temptation” (en kairôi peirasmou) for these superficial, emotional people who have to be periodically rounded up if kept within the fold.