It's a case of "spiritual caprice" when Christians get grumpy and complain about the path being pointed out to them after God offers salvation all the time and in so many ways, he said at the Mass in the Domus Sanctae Marthae March 24.

"Many times we say we are sick of the divine way. To not accept God's gift with his way -- this is sin, this is venom," he said, according to Vatican Radio.

The Pope's homily looked at the day's reading from the Book of Numbers (21:4-9) in which the people of Israel complain against God and Moses about being weary from their escape from slavery and the lack of water and decent food. After God sends venomous snakes, which kill many of the people as punishment, he tells Moses to make a bronze serpent mounted on a pole that will bring life to those who have been bitten.

Pope Francis said the staff with the serpent is a symbol of the cross upon which Jesus will be raised and which will become a source of salvation from the venom of sin for all those who look upon it.

How many Christians today "do we find a bit poisoned with dissatisfaction in life," he said, those about to "die in the desert of their sadness, their grumbling, their not wanting God's way."

These so-called "half-Christians" say, "Yes, it's true, God is good, but ...," the Pope said.

They do not go all the way "to open their hearts to God's salvation. They always try to put conditions on it: 'Yes, but this way. Yes, yes, I want to be saved, but by taking this path.' This is how the heart becomes poisoned" with venom, he said.

The venom "poisons our soul, it takes joy away from you, it doesn't let you go" and be free, he added.

But when Jesus was nailed to the cross, he took all that venom and sin upon himself, the Pope said.

"This lukewarm soul, this being half-Christian, 'Christians, yes, but ...,' this enthusiasm at the start of the journey with the Lord that then becomes dissatisfied, this is only healed when looking at the cross, looking at God who takes on our sins: my sin is there."

The Pope asked people to look at "the serpent, the venom -- there, in the body of Christ -- the venom of all the sins of the world, and let us ask for the grace to accept difficult moments, to accept the divine way of salvation," to accept the wretched sustenance the people of Israel complained about and all the ways "the Lord is bringing me forward."

Pope Francis prayed that the liturgies of Holy Week -- the week before Easter Sunday -- would "help us escape from this temptation of becoming 'Christians, yes, but. ...'"