Not just a man-made idea. God understood it was well and His word shows to to practice true religion.
1 Timothy 5:4
But if a widow has children or grandchildren, these should learn first of all to put their
religion into practice by caring for their own family and so repaying their parents and grandparents, for this is pleasing to God.
James 1:26
Those who consider themselves
religious and yet do not keep a tight rein on their tongues deceive themselves, and their
religion is worthless.
James 1:27
Religion that God our Father
accepts as pure and faultless is this: to look after orphans and widows in their distress and to keep oneself from being polluted by the world.
There's only 5 occurances of the English word "religion" in the KJV Bible. Only once is it used in the positive sense regarding belief on Christ Jesus.
Acts 26:5
5 Which knew me from the beginning, if they would testify, that after the most straitest sect of our religion I lived a Pharisee.
(KJV)
Gal 1:13
13 For ye have heard of my conversation in time past in the Jews' religion, how that beyond measure I persecuted the church of God, and wasted it:
(KJV)
Gal 1:14
14 And profited in the Jews' religion above many my equals in mine own nation, being more exceedingly zealous of the traditions of my fathers.
(KJV)
James 1:26-27
26 If any man among you seem to be religious, and bridleth not his tongue, but deceiveth his own heart, this man's religion is vain.
27
Pure religion and undefiled before God and the Father is this, To visit the fatherless and widows in their affliction, and to keep himself unspotted from the world.
(KJV)
And per the Greek word for "religion", it's Greek root is about piety. We are to practice piety, which is in the same sense of practicing holiness. Not appearing holy, but putting into practice the things of God that He approves of, which is what James' Message about "Pure religion" is about.
But what do MEN'S DOCTRINES say instead of that? They push their own DOCTRINES as a replacement for Pure religion, which is actually an attempt to replace what GOD Himself deems holy and just.