43 In the Hebrew text this causal clause comes at the end of the sentence. The translation alters the word order for stylistic reasons. Because you have obeyed me. Abraham’s obedience brought God’s ratification of the earlier conditional promise (see Gen 12:2).
44 Traditionally the verb is taken as passive (“will be blessed”) here, as if Abraham’s descendants were going to be a channel or source of blessing to the nations. But the Hitpael is better understood here as reflexive/reciprocal, “will bless [i.e., pronounce blessings on] themselves/one another” (see also Gen 26:4). Elsewhere the Hitpael of the verb “to bless” is used with a reflexive/reciprocal sense in Deut 29:18; Ps 72:17; Isa 65:16; Jer 4:2. Gen 12:2 predicts that Abram will be held up as a paradigm of divine blessing and that people will use his name in their blessing formulae. For examples of blessing formulae utilizing an individual as an example of blessing see Gen 48:20 and Ruth 4:11. Earlier formulations of this promise (see Gen 12:2; 18:18) use the Niphal stem. (See also Gen 28:14.)

In other versions

and in your offspring shall all the nations of the earth be blessed, because you have obeyed my voice.”

and through your offspring all nations on earth will be blessed, because you have obeyed me.”

And all the nations of the earth will be blessed by your offspring because you have obeyed my command.”

And through your descendants all the nations of the earth will be blessed—all because you have obeyed me.”

All the nations of the earth will be blessed through your offspring, because you have listened to my voice.”

And in thy seed shall all the nations of the earth be blessed; because thou hast obeyed my voice.

Public Domain