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Zeal, true zeal, comes from the Father above and enables a man of God to do the work of God and persevere.
Merriam-Webster Online Dictionary (inspiring zeal) enthusiasm:
Etymology: Greek enthousiasmos, from enthousiazein to be inspired, irregular from entheos inspired, from en- + theos god
1 a : belief in special revelations of the Holy Spirit (i.e.) indwelling of the Holy Spirit.

But ye shall receive power, after that the Holy Ghost is come upon you: and ye shall be witnesses unto me both in Jerusalem, and in all Judaea, and in Samaria, and unto the uttermost part of the earth. Acts 1:8
But the Comforter, which is the Holy Ghost, whom the Father will send in my name, he shall teach you all things, and bring all things to your remembrance, whatsoever I have said unto you. John 14:26

Zeal is that quality that infuses true delight in doing a task much like little children delighting in what they do.
Even so ye, forasmuch as ye are zealous of spiritual gifts, seek that ye may excel to the edifying of the church. 1 Corinthians 14:12

Ambition is not zeal.
Zeal is of the Spirit and ambition is of the flesh.
Merriam-Webster Online : ambition Function: noun Text: 1 strong desire for self advancement

(For Example of how a man of ambition hindered the work of Christ.)
3 John 1:9  ¶I wrote unto the church: but Diotrephes, who loveth to have the preeminence among them, receiveth us not.
10  Wherefore, if I come, I will remember his deeds which he doeth, prating against us with malicious words: and not content therewith, neither doth he himself receive the brethren, and forbiddeth them that would, and casteth them out of the church.
11  Beloved, follow not that which is evil, but that which is good. He that doeth good is of God: but he that doeth evil hath not seen God.

Ambition is born of a selfish desire to advance oneself and is an attribute of the most wicked men of all generations.
Adoph Hilter and Nero for instance.

Zeal and ambition are in opposition to each other.
¶Though the LORD be high, yet hath he respect unto the lowly: but the proud he knoweth afar off. Psalms 138:6

Zeal results in a meek and gentle behavior while ambition results in a proud and aggressive behavior.
Who gave himself for us, that he might redeem us from all iniquity, and purify unto himself a peculiar people, zealous of good works. Titus 2:14

To those who have become lukewarm in their Christian walk, Jesus said "Be zealous therefore and repent."
Rev 3:19
As many as I love, I rebuke and chasten: be zealous therefore, and repent.

Unless you be as little children you can in no way be a part of the work of the Kingdom of Heaven.
Mat 18:3
And said, Verily I say unto you, Except ye be converted, and become as little children, ye shall not enter into the kingdom of heaven.

Ask God to restore your zeal and He will.
Restore unto me the joy of thy salvation; and uphold me with thy free spirit. Psalms 51:12