Which will it be, God or money? The God spoken about in this context is the Father, the Son, and the Holy Spirit; one God in three persons. Money, or mammon, on the other hand, is any earthly means of exchange or gain (i.e., possessions).
While speaking with His disciples, the Lord Jesus Christ was overheard by the religious rulers of the day. They scoffed at what He said to His disciples:
“No servant can serve two masters, for either he will hate the one and love the other, or he will be devoted to the one and despise the other. You cannot serve God and money.” Luke 16:13 English Standard Version (ESV)
Christ then turned to these rulers and addressed how their heart attitudes kept them out of His Kingdom.
Christ spoke the same words to a different audience who listened intently to His Sermon on the Mount. He spoke about the heart attitude that His disciples and the crowds that followed Him should possess in the Kingdom of God. As part of that sermon, Christ said:
“No one can serve two masters, for either he will hate the one and love the other, or he will be devoted to the one and despise the other. You cannot serve God and money.” Matthew 6:24 (ESV)
Although the disciples were common to both groups, many in the first audience sneered at what He said and in the second, they hung on His every word.
No man can serve two masters. …[Christ] had formerly said, that the heart of man is bound and fixed upon its treasure; and he now gives warning, that the hearts of those who are devoted to riches are alienated from the Lord.
For the greater part of men are [inclined] to flatter themselves with a deceitful pretense, when they imagine, that it is possible for them to be divided between God and their own lusts. Christ affirms that it is impossible for any man to obey God, and, at the same time, to obey his own flesh…
We commonly call this a ‘divided heart.’ Calvin goes on:
True, it is not impossible that those who are rich shall serve God; but whoever gives himself up as a slave to riches must abandon the service of God: for covetousness makes us the slaves of the devil…
So it isn’t the riches themselves, so much as setting our hearts on those riches to the partial (or total) exclusion of Him. Calvin then extends this principle to all our vices.
…As God pronounces everywhere such commendations of sincerity, and hates a double heart, (1 Chronicles 12:33; Psalm 12:2); all are deceived, who imagine that he will be satisfied with the half of their heart…
The covetous, the voluptuaries, the gluttons, the unchaste, the cruel, all in their turn offer the same apology for themselves: as if it were possible for those to be partly employed in serving God, who are openly carrying on war against him.
It is, no doubt, true, that believers themselves are never so perfectly devoted to obedience to God, as not to be withdrawn from it by the sinful desires of the flesh.
But as they groan under this wretched bondage, and are dissatisfied with themselves, and give nothing more than an unwilling and reluctant service to the flesh, they are not said to serve two masters: for their desires and exertions are approved by the Lord, as if they rendered to him a perfect obedience.
But this passage [Luke 16:13] reproves the hypocrisy of those who flatter themselves in their vices, as if they could reconcile light and darkness.
So there we have it. The question now becomes: “Do I serve the devil or do I serve the Lord.” For, we all have to serve somebody.