Exodus 15:2 = "'The LORD is my strength and my defense [or song]; he has become my salvation. He is my God, and I will praise him; my father's God, and I will exalt him." (Moses's and the Israelite's song after Moses parted the sea)
Isaiah 12:2 = "Surely God is my salvation; I will trust and not be afraid. The LORD, the LORD himself, is my strength and my song [or defense]; he has become my salvation.'" (Isaiah's reference to Exodus 15:2 and prophecy for the repentance and joy of the remnant of Israel after God's wrath as well as His providence and salvation)
What does it mean for God to be one's song? Think about it: The LORD, the LORD himself, is my strength and my song. The repeating of the phrase "the LORD" gives emphasis and a greater weight in the Hebrew writing style to the fact that it is God, nothing else, who is "my strength and my song."
He is my strength; I think I get that. I've seen it in Philippians 4:13 ("I can do all this [or things] through him [Christ] who gives me strength"), and I understand that He is the ultimate source of my strength, my love, my everything, along with the fact that He will never give me any situation greater than I can handle with His help (related to 1 Cor. 10:13). But my song?
Switchfoot sings worshipfully in "Your Love is a Song" that God's love is a symphony and a melody coursing completely through oneself. I suppose one could say that since God is love, God Himself therefore is a song. But I'm not 100% satisfied. I think it goes a little bit deeper.
And this may not necessarily be correct, because I'm writing and thinking and guessing and making a hypothesis I suppose all at once...but of course, this is my blog, not yours, dear reader, so I can say what I want. You're welcome to comment below and lend me your views though!
But here's what I think either way: I think more than God being love and His love being a song, God is a song. Period. He is this incredible, uncontainable, incomparable, hard-to-comprehend, ultimately divine being who is greater than anyone can possibly imagine with a faulty human mind. He breathes life into things and holds the universe in His hands, having created time and space and the life within it. He ultimately, by way of being who He is, is a song, in the sense that all His creation was made to reflect Him in a glorious symphony.