John Gill

And therefore it was imputed to him for righteousness. Not because his faith was strong, and he had a full assurance of it, but because it was right, resting on the promise of God, and relying upon his power and faithfulness to perform it; for though the righteousness of faith is not imputed to any sort of believers, not to mere nominal ones, yet to all such as have true faith, though it may be but weak; for faith, as to nature, kind, and object, though not as to degree, is the same in all true believers, and the same righteousness is imputed to one as to another. And therefore it was imputed to him for righteousness. Not because his faith was strong, and he had a full assurance of it, but because it was right, resting on the promise of God, and relying upon his power and faithfulness to perform it; for though the righteousness of faith is not imputed to any sort of believers, not to mere nominal ones, yet to all such as have true faith, though it may be but weak; for faith, as to nature, kind, and object, though not as to degree, is the same in all true believers, and the same righteousness is imputed to one as to another. Romans 4:23 rom 4:23 rom 4:23 rom 4:23Now it was not written for his sake alone,.... This was not left on the sacred records, Gen 15:6, that it was imputed to him; purely on his account, merely for his sake, as an encomium of his faith, and an honourable testimony to it, and for the encouragement of it; though this was doing him a very great honour, and was one design of it.