Evil is prevalent, and Christians must guard themselves against the devil, Pope Francis warned yesterday.

Speaking in St Peter's Square on the first Sunday of the new year, the Pope spoke on the first chapter of John's Gospel.

"'The Word' – that is, the creative Word of God – 'was made flesh, and dwelt among us'," he said.

"That Word which dwells in heaven... came to earth so that we might listen and be able to know and touch with our hand the love of the Father.

"The Word of God is himself the only-begotten Son, made man, full of love and of faithfulness, Jesus himself."

Francis said the passage offers Christians an opportunity to "welcome this Word of salvation, this mystery of light".

"If we welcome him, if we welcome Jesus, we will grow in understanding and in the love of the Lord, we will learn to be merciful as He is."

He suggested that this is particularly poignant as Catholics enter into the Holy Year of Mercy.

However, the "mystery of evil... demands vigilance and care on our part so that it will not prevail," the Pope continued.

"The book of Genesis says – in a good phrase that makes us understand this – it says that evil 'lies in wait at our door'. Woe to us if we allow it to enter; it would then close our door to anyone else. Instead we are called to throw open the door of our heart to the Word of God, to Jesus, in order thus to become His children."

The devil is "always lying in wait by our door, and wants to enter," he added, but Jesus "will defend us from evil, from the devil."

Pope Francis also encouraged the thousands gathered to spend time reading the Bible every day. "Meditating on it and incarnating it in daily life is the best way to understand Jesus and bring Him to others," he said.

"Keeping a little Gospel in your pocket or purse will do you good. Never forget: Let's read a passage from the Gospel each day."