"Then sang Moses and the children of Israel this song unto The Lord, and spake, saying, I will sing unto The Lord, for He hath triumphed gloriously: the horse and his rider hath He thrown into the sea. The Lord is my strength and song, and He is become my salvation: He is my God, and I will prepare Him an habitation; my fathers God, and I will exalt Him. The Lord is a man of war: The Lord is His name."
The backstory to the song in Exodus 15 is that the Israelites were fleeing the Egyptians, when they were met by the Red Sea. God through Moses parted the sea and Israel passed through unharmed. When the Egyptians armies came, it closed back in on them. "...the horse, and his rider hath He thrown into the sea..."
In their victory, Moses and the Israelites praised The Lord by singing a song which reflected the events which had taken place.
The key message in Exodus 15:1-3 is that The Lord is our Salvation!
In Exodus 15:1 the people offer singing up to the Lord saying, "...I will sing unto The Lord, for He hath triumphed gloriously." They then in verse 2 promise to prepare a habitation for Him. "...I will prepare Him and habitation..."
The singers state that strength, salvation and their God are theirs through The Lord. These things are also ours through Him. We should thank Him and sing in thanksgiving and worship for what He has done in our life.