In 1 Corinthians 12...our Apostle Paul says that God
had put each member of the Body of Christ here for a
specific purpose:

v. 14 "For the body is not one member, but many... But
now hath God set the members every one of them in the
body, as it hath pleased him. 19 And if they were all
one member, where were the body? 20 But now are they
many members, yet but one body."

Included in these members are men who are sent by God
to preach and teach His Word:

1 Cor 3..."Who then is Paul, and who is Apollos, but
ministers by whom ye believed, even as the Lord gave to
every man?"

1 Cor 1..."For after that in the wisdom of God the
world by wisdom knew not God, it pleased God by the
foolishness of preaching to save them that believe."

Rom 10..." How then shall they call on him in whom they
have not believed? and how shall they believe in him of
whom they have not heard? and how shall they hear
without a preacher?"

The way God "calls" anyone is He uses His Providence,
that is, He indirectly intervenes in their lives thru
His Spirit in them (given to them the moment they are
saved), and His Word in them (as they grow and mature
in Pauline Grace Doctrine) to motivate them to serve
Him.

So the way that God has "called" me to preach is thru
His Word giving me the deep desire to preach and teach
and lead others in these truths.

He also motivates me as well thru other saints asking
me to do preach to them, and appreciating my labour in
the Word and doctrine.

God ordains men to leadership positions (called elders)
to guide the saints in His Word, and some of those men,
God gives the intense desire and ability to
teach/preach His Word:

Titus 1...For this cause left I thee in Crete, that
thou shouldest set in order the things that are
wanting, 2 and ordain elders in every city, as I had
appointed thee:

1 Tim 3...1 This is a true saying, If a man desire the
office of a bishop, he desireth a good work.

2 Tim 2...Thou therefore, my son, be strong in the
grace that is in Christ Jesus. 2 And the things that
thou hast heard of me among many witnesses, the same
commit thou to faithful men, who shall be able to teach
others also.

So I believe that I am "called" of God to teach and
preach because over the years of being a believer I
have had the intense desire from God's Word to not only
labour in studying the Word of God, but God has made me
very good in delivering it, and making it clear for
others to understand!