The Muslims will be the Ones Who gain in the Hereafter

Here Allah tells us that His believing servants, who recite and believe in His Book, and do the deeds prescribed in it such as establishing regular prayer at the prescribed times, night and day, spending (in charity) out of that which Allah has provided for them secretly and openly,

(they hope for a (sure) trade-gain that will never perish.) means, they hope for a reward from Allah which will inevitably be theirs. Allah says:

(That He may pay them their wages in full, and give them (even) more, out of His grace.) meaning, that He may give them a reward for what they have done, and multiply it by adding more, such as has never occurred to them.

(Verily, He is Oft-Forgiving,) means, He forgives their sins,

(Most Ready to appreciate.) means, He appreciates even a little of their good deeds.