Albert Barnes Commentary Haggai 1:13

"Then spake Haggai Jehovah`s messenger in Jehovah`s message unto the people, saying, I am with you, saith Jehovah." — Haggai 1:13 (ASV)

And Haggai, the Lord’s messenger - Malachi, whose own name was framed to express that he was “the Lord’s messenger,” and Haggai alone uses the title, as the title of a prophet; perhaps as forerunners of the great prophet whom Malachi announced. Malachi also speaks of the priest as the messenger of the Lord of hosts (Malachi 2:7), and prophesies of John the Baptist as the messenger of the Lord (Malachi 3:1), who should go before His face. Haggai, as he throughout repeats that his words were God’s words, frames a new term to express, in the language of the New Testament (compare 2 Corinthians 5:20), that he had an embassy from God; this term is in the Lord’s message.

I am with you - All the needs and longings of the creature are summed up in those two words, I am with you. “Who are You and who am I? You, He Who Is; I, he who is not; nothing, indeed worse than nothing.” Yet, if God be for us (Romans 8:31), Paul asks, who can be against us? Our blessed Lord’s parting promise to the Apostles, and in them to the Church, was (Matthew 28:20): Lo I am with you alway, even to the end of the world.

The all-containing assurance goes beyond any particular promise of aid, such as, “I will help you, and will protect you, so that your building shall have its completion.” This is one fruit of it: “since I am in the midst of you, no one shall be able to hinder your building.” But, more widely, the words indicate His presence in love, who knows all our needs, and is Almighty to support and save us in all.

So David says (Psalms 23:4), when I walk through the valley of the shadow of death, I will fear no evil, for Thou art with me: and God says by another (Psalms 91:15), I will be with him in trouble, and by Isaiah (Isaiah 43:2), When thou passest through the waters, I will be with thee.