Isaiah reminding the people, in his hearing, of the power of God in their deliverance from Egypt hundreds of years prior to this day of which he is speaking.

The song is still good for the Christian and one that needs to be expressed and remembered continually. God is still Holy, Righteous, and Just. He is worthy of our worship and praise.

And in that day thou shalt say, O LORD, I will praise Thee: though Thou wast angry with me, Thine anger is turned away, and Thou comfortedst me.
Behold, God is my salvation; I will trust, and not be afraid: for the LORD JEHOVAH is my strength and my song; He also is become my salvation. Therefore with joy shall ye draw water out of the wells of salvation. And in that day shall ye say, “Praise the LORD,” call upon His name, declare His doings among the people, make mention that His name is exalted.
Sing unto the LORD; for He hath done excellent things: this is known in all the earth. Cry out and shout, thou inhabitant of Zion: for great is the Holy One of Israel in the midst of thee.

Isaiah 12:1-6

Do we as Christians remember from where we came? Do we remember the way we were before we called on the name of Jesus, and was born again?

The way we often speak evil words, and sow evil thoughts, and treat other people it seems that we have. If we are honestly seeking to glorify the LORD with our lives let us make our lives a song of praise and worship. Being filled continually with the Holy Spirit we will sing songs, and make melody in our hearts to the Lord, submitting to Him in all things. Husbands will love their wives as Christ loved the Church and give Himself for her; and wife will submit to her husband. Children will be obedient to their parents. Fathers will not provoke their children to wrath. Employees will do their work as unto the Lord. Employers will pay their employees well, and bless them (Ephesians 5:18-6:24). These are evidences of one filled with the Spirit.

Words of praise and worship to the Lord, singing them to the Lord, with a heart for Him comes from the Spirit of God the Holy Spirit. Everyone who has been born again has the Holy Spirit living within them, but we are not always filled with the Spirit, and that is mostly because we have let sin enter our lives. Keeping short accounts with God is a necessity when it comes to our sin against Him.

God the LORD of hosts is the Holy One of Israel is calling you to trust in Him, by believing in His only Son Jesus Christ who died for our sins on the cross, He was buried carrying our sins away. and He arose and came out alive forever more.