Matthew 14:29 And he said, Come. And when Peter was come down out of the ship, he walked on the water, to go to Jesus.
30 But when he saw the wind boisterous, he was afraid; and beginning to sink, he cried, saying, Lord, save me.31 And immediately Jesus stretched forth his hand, and caught him, and said unto him, O thou of little faith, wherefore didst thou doubt?
When Peter faith was constant he walked on water, until he doubted, it is important to know, as fish is born in water so a Christian is born in the realm called faith. Heb 10:38 Now the just shall live by faith. As fish would die when taken out of water the same principle apply to a Christian taken out of faith.
The only way to please God in the Bible is by faith; Heb 11:6 But without faith it is impossible to please him: for he that cometh to God must believe that he is. Without faith one is made a sinner Rom 14;23 whatsoever is not of faith is sin.
Even for the prayer of a believer to be heard by God faith got to be applied, James 1: 6 But he must ask in faith, without any doubts, for the one who has doubts is like a wave of the sea that is driven and tossed by the wind. 7 Such a person should not expect to receive anything from the Lord.
Knowing this things then what a manner of person ought you to be 2 Peter 3:11 what manner of persons ought ye to be?
Therefore holy brethren let your faith be constant and fight for your faith, earnestly contend for your faith. Jude 1:3 earnestly contend for the faith which was once delivered unto the saints.
A child of God should understand we walk by faith not by sight(2 Cor 5:7)Luke 18:8 Nevertheless when the Son of man cometh, shall he find faith on the earth?
Further study
Hebrew 11:1-40
Mark 11: 23
Mat 15:28
Mar 5:34 .
Luke 17:5