Serving mammon is done as long as one does not serve God wholeheartedly. As long as one's heart is divided in serving God, one is serving mammon. No man can serve two masters: for either he will hate the one, and love the other; or else he will hold to the one, and despise the other. Ye cannot serve God and mammon (Matthew 6:24). As long as one seeks to look back to earthly things even with the slightest desire, one is serving mammon and hating God. No man, having put his hand to the plough, and looking back, is fit for the kingdom of God (Luke 9:62). There is no argument, and neither can there be an argument about this. Anyone who seeks to argue against this is really rebelling against God because these are Jesus' words, not my words.
After telling the rich young ruler to sell all he had, Jesus turned to His disciples, warning them about how hard it is to enter the Kingdom of Heaven. He said, "It is easier for a camel to go through the eye of a needle, than for a rich man to enter into the kingdom of God
Ye lust, and have not: ye kill, and desire to have, and cannot obtain: ye fight and war, yet ye have not, because ye ask not (James 4:2).