COMMENTARY on 4:137
A. Yusuf Ali:

Translation:
Those who believe, then reject faith, then believe (again) and (again) reject faith, and go on increasing in unbelief,- Allah will not forgive them nor guide them nor guide them on the Way. 647
Commentary:

647  Those who go on changing sides again and again can have no real Faith at any time. Their motives are mere worldly double-dealing. How can they expect Allah's grace or forgiveness? Here is a clear warning against those who make their religion a mere matter of worldly convenience. True religion goes far deeper. It transforms the very nature of man. After that transformation it is as impossible for him to change as it is for light to become darkness.

 

Muhammad Asad:

Translation:
Behold, as for those who come to believe, and then deny the truth, and again come to believe, and again deny the truth, and thereafter grow stubborn in their denial of the truth 153 - God will not forgive them, nor will He guide them in any way.
Commentary:
153  Lit., "increase in a denial of the truth".