The correct answer to this open question is the following.
Although there are no options attached, we can say the following.
The significance of the kneeling angel at the left side of this painting is that it was painted by the great Leonardo Da Vinci when he was the disciple of his master Andrea Del Verrochio in 1472.
We are talking about the famous painting called "The Baptism of Christ." The participation of Da Vinci in the painting was that he gave the final touches to the painting and included the kneeling angel on the left side of the painting next to the other angel that had been painted by his master Verrocchio. The work was done for the Church of San Slavi, in Florence.