Because that Abraham obeyed my voice, and kept my charge, my commandments, my statutes, and my laws. Abraham obeyed my voice - מימרי meimeri, my Word. See Genesis 15:1.
My charge - משמרתי mishmarti, from שמר shamar, he kept, observed, etc., the ordinances or appointments of God. These were always of two kinds:
1. Such as tended to promote moral improvement, the increase of piety, the improvement of the age, etc. And
2. Such as were typical of the promised seed, and the salvation which was to come by him.
For commandments, statutes, etc., the reader is particularly desired to refer to Leviticus 16:15, etc., where these things are all explained in the alphabetical order of the Hebrew words.