So whoever Allah wants to guide – He expands his breast to [contain] Islam; and whoever He wants to misguide – He makes his breast tight and constricted as though he were climbing into the sky. Thus does Allah place defilement upon those who do not believe.
Meaning:-
Constricted:narrowed, especially by encircling pressure, to stultify, stop, or cause to falter.
Defilement: to make impure or unclean, to make foul, dirty.