Why we do not lose heart?

Because we are being transfigured into His image

And all of us, as with unveiled face, [because we] continued to behold [in the Word of God] as in a mirror the glory of the Lord, are constantly being transfigured into His very own image in ever increasing splendor and from one degree of glory to another; [for this comes] from the Lord [Who is] the Spirit.” 2 Corinthians 3:18

For our light affliction of this present time are not compared to the eternal weight of Glory

“Therefore we do not lose heart. Even though our outward man is perishing, yet the inward man is being renewed day by day. 

For our light affliction, which is but for a moment, is working for us a far more exceeding and eternal weight of glory, 

while we do not look at the things which are seen, but at the things which are not seen. For the things which are seen are temporary, but the things which are not seen are eternal.”

II Corinthians 4:16-18 

We will reap in due time

"And let us not lose heart and grow weary and faint in acting nobly and doing right, for in due time and at the appointed season we shall reap, if we do not loosen and relax our courage and faint.”

Galatians 6:9

“And as for you, brethren, do not become weary or lose heart in doing right [but continue in well-doing without weakening].”

2 Thessalonians 3:13

“So I ask you not to lose heart [not to faint or become despondent through fear] at what I am suffering in your behalf. [Rather glory in it] for it is an honor to you.”

Ephesians 3:13 

“though He was a Son, yet He learned obedience by the things which He suffered. And having been perfected, He became the author of eternal salvation to all who obey Him,”

Hebrews 5:8-9

“For in that He Himself has suffered, being tempted, He is able to aid those who are tempted.”

Hebrews 2:18 

Amen