Ask your Sustainer to forgive you your sins, and then turn towards Him in repentance - [whereupon] He will grant you a goodly enjoyment of life [in this world] until a term set [by Him is fulfilled];4
and [in the life to come] He will bestow upon everyone possessed of merit [a full reward for] his merit.5
But if you turn away, then, verily, I dread for you the suffering [which is bound to befall you] on that awesome Day!6
I.e., "till the end of your lives" (for an explanation of the term ajal musamma, see note  on 6:2 ). Since God, in His unfathomable wisdom, does not always grant worldly happiness and material benefits to everyone who believes in Him and lives righteously, it is only reasonable to assume - as Rashid Rida' does in Manar XII, 7 ff. - that the "goodly enjoyment of life" (i.e., in this world) promised in the above sentence relates to the community of the believers as a whole, and not necessarily to individuals. (Cf. 3:139 - "you are bound to rise high if you are [truly] believers".)
The noun fadl, when used with reference to God, invariably denotes "bounty" or "favour"; in its reference to man, is usually signifies "merit" or, occasionally, "eminence". The above verse makes it clear that, in contrast to the partial and often only moral rewards and punishments in the life of this world, God will, in the life to come, bestow the full measure of His favours upon everyone who has acquired merit by virtue of his faith and his actions. (Cf. 3:185 - "only on the Day of Resurrection will you be requited in full for whatever you have done".)
Lit., "the suffering of a great Day". See in this connection 9:128 .