Malbim: They are four ways in which Hashem stuck Yisrael to Himself. (a) They will be a nation to me - corresponding to buying the Ezor. (b) Wearing the Ezor earns one distinction and publicity, so Yisrael were to Hashem. (c) An Ezor is a sign of strength - so Yisrael were for praise. (d) Linen is a sign of glory - so were Yisrael.