Not a hymn to sing sitting down! These are the words of an American by the name of George Duffield (1818‑1888). He lived in many states in the North East of that country including 7 years in then 1840s as a Presbyterian Minister in Brooklyn. He wrote this in 1858 inspired by the dying words of a Christian who said, "Tell them to stand up for Jesus: now let us sing a hymn". According to hymnary.org the background to this was slavery.

Here are some verses from the Bible that are reckoned to have inspired the writer;

2 Tim.2:3 Therefore endure hardness, as a good soldier of Jesus Christ.

1 Corinthians 15:25‑27 For he must reign, till he hath put all enemies under his feet. The last enemy that shall be destroyed is death. For he hath put all things under his feet.

Psalm 144:1‑2 Blessed be the LORD my strength which teacheth my hands to war, and my fingers to fight: my goodness, and my fortress; my high tower, and my deliverer; my shield, and he in whom I trust; who subdueth my people under me.

Phil.2:11 That every tongue should confess that Jesus Christ is Lord, to the glory of God the Father.

Rom.14:4 Yea, he shall be holden up: for God is able to make him stand.

2 Chron.32:8 With him is an arm of flesh; but with us is the LORD our God to help us, and to fight our battles. And the people rested themselves upon the words of Hezekiah king of Judah.

Eph.6:10‑17 Brethren, be strong in the Lord, and in the power of his might. Put on the whole armour of God, that ye may be able to stand against the wiles of the devil. For we wrestle…against principalities, against powers, against the rulers of the darkness of this world… Wherefore take...the whole armour of God, that ye may be able to withstand in the evil day, and having done all, to stand. Stand therefore, having your loins girt about with truth, and having on the breastplate of righteousness; and your feet shod with the preparation of the gospel of peace; above all, taking the shield of faith, wherewith ye shall be able to quench all the fiery darts of the wicked. And take the helmet of salvation, and the sword of the Spirit, which is the word of God.

1 Cor.16:13 Watch...stand fast in the faith, quit you like men, be strong.

1 Cor.14:8 For if the trumpet give an uncertain sound, who shall prepare himself to the battle?

1 John 5:4‑5 For whatsoever is born of God overcometh the world: and this is the victory that overcometh the world, even our faith. Who is he that overcometh the world, but he that believeth that Jesus is the Son of God?

Rev.2:10 Be thou faithful unto death, and I will give thee a crown of life.

2 Tim.4:7‑8 I have fought a good fight, I have finished my course, I have kept the faith: henceforth there is laid up for me a crown of righteousness, which the Lord,...shall give me...and...all them also that love his appearing.

Rev.3:21 To him that overcometh will I grant to sit with me in my throne, even as I also overcame, and am set down with my Father in his throne.

The most common tune is called either ‘Morning Light’ or ‘Webb’ as it was composed by George Webb (1803‑1887) born Salisbury, Wiltshire.