The first part of this verse extends the meaning of the curse, while the second part adds something more to the curse.

When you till the ground: till is as in 2.5. No longer yield to you its strength means “it [the ground] will not produce or grow anything.” According to Anchor Bible this is a poetic use of strength for “produce”; Revised English Bible has “its produce” and New International Version “its crops.” Good News Translation combines both of these senses: “… crops, the ground will not produce anything.” Negatively we may say “the soil will be sterile, infertile, unproductive.” One good example from an existing translation says “The ground will withhold its goodness, and food will not be able to grow in it.” Another says “The ground will not fruit its fruits for you any more.”

You shall be a fugitive and a wanderer on the earth: a fugitive and a wanderer translates two similar-sounding Hebrew participles linked by “and,” a construction that suggests, according to some, a single idea, and so “homeless wanderer” (Good News Translation and Anchor Bible). Others treat the two words as separate ideas. For example, Revised English Bible “a wanderer, a fugitive on the earth.” Fugitive here suggests fleeing or escaping from God and from people. The word rendered wanderer refers in other contexts to a person’s unstable movements, as in “to totter” or “to stagger.” On the earth refers to the whole world and emphasizes the extent of Cain’s punishment: he will have no home anywhere, and he will have to wander everywhere. This part of the curse means that Cain will be cut off from his family and relatives. Bible en français courant says “You will be uprooted, always roaming over the earth.” This may also be translated “You will be without a home and always drifting everywhere.”

In trying to express the meaning of this Hebrew phrase, many translations include three elements:
(1) Cain will have no place or home of his own;
(2) he will be a “traveler,” always on the move;
(3) he will keep on going round and round, all over the world or to every place in the world.

Quoted with permission from Reyburn, William D. and Fry, Euan McG. A Handbook on Genesis. (UBS Helps for Translators). New York: UBS, 1997. For this and other handbooks for translators see here .