He is thy life, i.e. the cause or author of thy life, as life is used 1 Thessalonians 14:6, 1 Thessalonians 17:3.
Related Commentaries of Deuteronomy 30:20
Deuteronomy 30:20
20 That thou mayest love the LORD thy God, and that thou mayest obey his voice, and that thou mayest cleave unto him: for he is thy life, and the length of thy days: that thou mayest dwell in the land which the LORD sware unto thy fathers, to Abraham, to Isaac, and to Jacob, to give them.